This is a rough status assessment of unknowns that will ultimately be determined at the 2021 U.S. Olympic Team Trials in track and field, which can be seen live June 18-27 on NBCOlympics.com, the NBC Sports app, connected devices and the networks of NBCUniversal.

Allyson Felix (USA)

2016 Olympics: S, 400m (49.51); G, 4x100m relay; G, 4x400m relay

2017 Worlds: B, 400m (50.08); G, 4x100m relay; G, 4x400m relay

2019 Worlds: G, 4x400m mixed relay; G, 4x400m relay

Tied with Jamaica's Merlene Ottey for the title of most decorated female track and field athlete in Olympic history at nine medals apiece, the United States' Allyson Felix is aiming for her fifth Games appearance and the first as a mother after giving birth to daughter Camryn in November 2018. The 35-year-old, whose female record six Olympic track and field golds is behind only four male track and field athletes' totals, hasn't stopped collecting medals since the 2016 Rio Olympics — her combined four titles plus a bronze at the two intermediate world outdoor track and field competitions made her the most decorated athlete male or female in World Athletics championship history, a feat she accomplished at 2017 worlds in London. To summarize, Felix has nine Olympic medals with six golds and 18 worlds medals with 13 golds.

Felix has gradually moved up in sprint distance over the years, having moved up to focus on the 400m in 2016 and not since the 2017 season regularly run the 100m and 200m. Five of her six Olympic titles are from the 4x100m and 4x400m relays. After helping Team USA win the 4x100m relay and 4x400m mixed relay at the 2019 world championships in Doha, Qatar, Felix and her teammates will again be the favorites to bring home Olympic golds in those events. The 4x100m relay looks to be a lock for Jamaica and it's unlikely Felix will rejoin that team, one with which she set the world record at the 2012 London Games and won the 2017 world title but didn't run it in Doha. An individual appearance is possible in the 400m but Felix faces stiff competition not only at the world stage but at her own trials, which is often the case for U.S. track athletes, particularly sprinters. As of late March 2021 she was ranked No. 18 with six fellow Americans ahead.

Christian Taylor and Will Claye (USA)

Christian Taylor

2016 Olympics: G, Triple Jump (17.86m)

2017 Worlds: G, Triple Jump (17.68m)

2019 Worlds: G, Triple Jump (17.92m)

Will Claye

2016 Olympics: S, Triple Jump (17.76m)

2017 Worlds: S, Triple Jump (17.63m)

2019 Worlds: S, Triple Jump (17.74m)

The University of Florida turned Team USA triple jumping duo of Christian Taylor and Will Claye is unlike anything the sport has ever seen. Going into the Tokyo Games the Americans are both the two-time Olympic champion and runner-up from 2012 and 2016 and the two-time reigning world champion and runner-up from 2017 and 2019. Each of those four competitions has seen Taylor and Claye go 1-2, respectively. Looking back in Olympic history alone, there are only eight other instances in which two athletes have kept the same gold and silver order in an individual event in consecutive Games — 1948 to 1952: USA's Mal Whitfield and Jamaica's Arthur Wint in the men's 800m, and Czechoslovakia's Emil Zatopek and France's Alain Mimoun in the men's 10,000m; 1998 to 1992: USA's Carl Lewis and Mike Powell in the men's long jump; 1996 to 2000: Czech Republic's Jan Zelezny and Great Britain's Steve Backley in the men's javelin, and Ethiopia's Haile Gebrselassie and Kenya's Paul Tergat in the men's 10,000m; 2004 to 2008: Jamaica's Veronica Campbell-Brown and USA's Allyson Felix in the women's 200m, and Ethiopia's Kenenisa Bekele and Sileshi Sihine in the 10,000m; and 2008 to 2012: Czeck Republic's Barbora Spotakova and Germany's Christina Obergfoll in the women's javelin. Only two – Lewis-Powell and Bekele-Sihine – were compatriots like Taylor and Claye. No one has gone back-to-back-to-back.

Taylor for some time now has had his sights set on taking down Briton Jonathan Edwards' long-standing triple jump world record of 18.29m from the 1995 world championships. His personal best of 18.21m from the 2015 world championships came just 9 centimeters shy of breaking the record on its two-decade anniversary or thereabout. Taylor, who turns 31 shortly before Tokyo, hasn't surpassed 18 meters at a major competition since jumping 18.11m in early 2017. But, as evidenced by his two world crowns since, the slight dip hasn't affected any title-winning.

Meanwhile, Claye, who's almost exactly one year younger than Taylor, cleared 18 meters in June 2019. The reigning world indoor champion's 18.14m recorded at a USATF meet in Long Beach, California, was the best triple jump mark since Taylor's 2015 PR and good enough for No. 3 all-time. Claye would again exceed 18 meters in Paris later that year. Progression-wise, Claye appeared as if he'd finally have an edge heading into the 2019 world championships in Doha, Qatar, but even after holding the lead through three rounds and a close call for Taylor, the 1-2 order endured.

Taylor and Claye are favorites once again to take gold and silver and do so for a historic third consecutive time.

Dalilah Muhammad and Sydney McLaughlin (USA)

Dalilah Muhammad

2016 Olympics: G, 400m hurdles (53.13)

2017 Worlds: S, 400mH (53.50)

2019 Worlds: G, 400mH (52.15); G, 4x400m relay

Sydney McLaughlin

2016 Olympics: 16th, 400mH (56.22)

2019 Worlds: S, 400mH (52.23); G, 4x400m relay

Dalilah Muhammad wasn't done after becoming the first American to win Olympic gold in the women's 400m hurdles at the Rio Games. After a silver medal in the event at the 2017 world championships, she took down its world record from 2003 at the 2019 USATF Outdoor Championships, running 52.20 to best Yuliya Pechonkina's 52.34. But she still wasn't done. Later that year at the 2019 world championships in Doha, Qatar, Muhammad lowered her own world record by four-hundredths of a second en route to winning her first gold at worlds. She would add another gold in the 4x400m relay.

Together with her on the winning 4x400m relay team in Doha was Sydney McLaughlin, a track prodigy one decade Muhammad's junior who was just 16 years old when she qualified for the Rio Games in 2016, competing later that summer about a week after turning 17. McLaughlin didn't fare as well Muhammad at her first Olympics, placing 16th overall in the 400m hurdles after an exit in the semifinals, but she would go on to finish the 2018 season with the best time in the world, and in Doha, go down to the line with Muhammad in a close finish to take silver. McLaughlin's time, 52.23, just seven-hundredths behind Muhammad's, put her No. 2 all-time.

This American matchup is bound to be one of the closest of the Games.

Other notables:

• World record-holder and two-time defending Olympic hammer throw champion Anita Wlodarczyk, 35, of Poland, who has all of the event's top 15 best marks
• World record-holder and defending Olympic marathon champion Eliud Kipchoge, 36, of Kenya, who set his historic 2:01:39 mark at the 2018 Berlin Marathon and broke Dennis Kimetto's 2014 time by 78 seconds
• World record-holder and reigning 3000m steeplechase world champion Beatrice Chepkoech, 29, of Kenya, who took down the 5K road world record in February
• Two-time defending Olympic discus champion Sandra Perkovic, 30, of Croatia, the 2017 world champion
• Defending Olympic 100m-200m double champion Elaine Thompson-Herah, 28, of Jamaica, and fellow countrywoman Shelly-Ann Fraser-Pryce, 34, a six-time Olympic medalist and the reigning world champion in the 100m who became a mother to Zyon in August 2017
• Defending Olympic shot put champion Ryan Crouser, 28, and reigning shot put world champion Joe Kovacs, 31, of the United States, both of whom swapped as runner-ups in those respective competitions, as well as 2017 shot put world champion Tom Walsh, 29, of New Zealand; they've all thrown 22.90m or better since 2019, and are the only ones to do so since 1990
• Reigning 1500m and 10,000m world champion Sifan Hassan, 28, of the Netherlands, the only athlete to accomplish the unprecedented double at a worlds or Olympics; also broke the mile world record in 2019
• Two-time reigning outdoor and indoor triple jump world champion Yulimar Rojas, 25, of Venezuela, the silver medalist in Rio and event's indoor world record-holder
• Two-time defending Olympic 5000m-10,000m double champion Mo Farah, 38, of Great Britain, who after Rio initially shifted his focus to the marathon but has since said he will focus on defending his 10K crown in Tokyo; Farah hasn't run a track 10K at a major meet since 2017
• World record-holder and defending Olympic 400m champion Wayde van Niekerk, 28, of South Africa, who hasn't gone sub-45 at a major meet since 2017
• Two-time reigning pole vault world champion Sam Kendricks, 28, of the U.S., the bronze medalist in Rio
• Reigning 100m hurdles world champion Nia Ali, 32, of the United States, the silver medalist in Rio
• Four-time reigning hammer world champion Pawel Fajdek, who failed to mark at the London Olympics and didn't make it out of the qualification phase in Rio
• Defending Olympic 400m champion Shaunae Miller-Uibo, 26, of the Bahamas, the 2019 world runner-up
• Five-time Olympic medalist Justin Gatlin, 39, of the United States, who took silver in the 100m at both the Rio Games and 2019 world championships
• Two-time reigning shot put world champion Gong Lijiao, 32, of China, who missed the Rio podium by less than a half-meter, and defending Olympic shot put champion Michelle Carter, 35, of the United States
• Defending Olympic long jump champion Tianna Bartoletta, 35, of the United States, her fellow countrywoman Brittney Reese, 34, Rio runner-up and 2017 long jump world champion, and reigning long jump world champion Malaika Mihambo, 27, of Germany, who missed the Rio podium by 13 centimeters
• Two-time reigning 5000m world champion Muktar Edris, 27, of Ethiopia, who was DQ'd at the Rio Games
• Defending Olympic 1500m champion and 2017 world champion Faith Kipyegon, 27, of Kenya, who took silver at the most recent world championships in Doha
• World record-holder and 2017 decathlon world champion Kevin Mayer, 29, of France, who was the silver medalist at the 2016 Rio Olympics
• Two-time reigning 5000m world champion Hellen Obiri, 31, of Kenya, the silver medalist in Rio
• Defending Olympic pole vault champion and 2017 pole vault world champion Katerina Stefanidi, 31, of Greece, and American Sandi Morris, 28, the silver medalist in Rio and at 2017 and 2019 worlds
• Two-time reigning high jump world champion Mutaz Essa Barshim, 29, of Qatar, the runner-up in Rio, and defending Olympic champ Derek Drouin, 31, of Canada
• Rio steeplechase bronze medalist Emma Coburn, 30, of the U.S., worlds 2017 champion and 2019 runner-up
• Reigning 200m world champ Dina Asher-Smith, 25, of Great Britain, who also took 100m silver at 2019 worlds
• Also: Jeff Henderson (USA), Katarina Johnson-Thompson (GBR), DeAnna Price (USA), Johannes Vette (GER), Matthew Centrowitz (USA), Kerron Clement (USA), Omar McLeod (JAM), Galen Rupp (USA), Ajee Wilson (USA), Kirani James (GRN), Jenny Simpson (USA), LaShawn Merritt (USA)

Usain Bolt (JAM)

The greatest sprinter of all time and world record-holder in the 100m and 200m effectively called it quits after the 2017 world championships in London, where he took a rare bronze in the 100m, his last individual race, scratched from the 200m and in an extraordinary turn of events pulled up in the final 100m of the 4x100m with what was later revealed as a torn hamstring. Bolt's eight Olympic gold medals are tied with the United States' Ray Ewry for the second most in track and field history, and his eight-for-eight perfect gold medal to total medal ratio is the best of any Olympian across all sports. He's also the only sprinter to ever win the 100m and 200m at back-to-back-to-back Games, the "triple-triple."

Bolt's electrifying presence will surely be missed at the Tokyo Games.

Ashton Eaton (USA) and Brianne Theisen-Eaton (CAN)

Multi-event power couple Ashton Eaton of the United States and Brianne Theisen-Eaton of Canada jointly announced their retirements both at the age of 28 following the new year in 2017. The Eatons, who met at the University of Oregon and married in 2013, were at the top of their games – Ashton was the decathlon world record-holder and had just defended his Olympic title at the Rio Games, while Brianne took heptathlon bronze in Rio.

Jessica Ennis-Hill (GBR)

A couple months after a silver in Rio, London Olympics heptathlete champion Jessica Ennis-Hill of Great Britain announced her retirement on social media in October 2016.

Ruth Beitia (ESP)

It isn't the first time the defending Olympic high jump champion has announced her retirement – she did so after taking fourth at the 2012 London Olympics. But frustrated with her lack of a medal, the Spaniard came back to competition and won gold in Rio at the age of 37 to become the oldest athlete to ever win an Olympic jumping event.

Christian Coleman (USA)

The reigning 100m world champion's absence in Tokyo is inarguably the most significant among athletes that were expected to be there. The Athletics Integrity Unit (AIU), which oversees anti-doping cases for World Athletics, charged Coleman in June 2020 with violating the anti-doping rules in connection with three whereabout failures within a 12-month period, which was subsequently upheld in October 2020 by an independent panel resulting in a two-year ban through May 2022.

Coleman's subsequent appeal to the Court of Arbitration for Sport (CAS) was partly upheld on April 15, 2021, resulting in a six-month reduction of the ban. His ineligibility period, now lasting 18 months, runs through Nov. 14, 2021, ending less than two months after the Tokyo Games.

Ruth Jebet (BRN)

The defending Olympic champion in the 3000m steeplechase was initially suspended in February 2018 then banned in March 2020 in relation to the Athletics Integrity Unit's (AIU) findings that evidence of "EPO," or blood doping, was allegedly collected in a urine sample in December 2017. Jebet, who was the event's world record-holder until her time was bested in 2018 by Beatrice Chepkoech, was also stripped of results from her positive test through the initial suspension. She's banned through February 2022.

Jemima Sumgong (KEN)

The defending Olympic marathon champion was accused in April 2017 by Athletics Integrity Unit (AIU) investigators of tampering with medical information in connection with a test finding that was allegedly positive for EPO, or blood doping. She was initially suspended before the full investigation was finished. The AIU eventually decided to impose an eight-year ban ending in January 2027.

Dilshod Nazarov (TJK)

The defending Olympic hammer throw champion was provisionally suspended in September 2019 after testing of samples from the 2011 world championships in Daegu, South Korea, allegedly showed presence of a prohibited substance. In March 2021, the Athletics Integrity Unit (AIU) imposed a two-year ban ending in September 2021. Nazarov's results between August 2011 and August 2013 were disqualified.

David Rudisha (KEN)

The 800m world record-holder and two-time defending Olympic champion presumably never thought the road to Tokyo would be easy, if he indeed decided to try and get there, but it's been particularly hazardous for the 32-year-old Kenyan. Among his obstacles: a quad muscle strain, back problems, his SUV colliding with a bus head-on in 2019 and a fractured left ankle with subsequent surgery in spring 2020. To top it all off, Rudisha hasn't raced in a major meet since July 2017 in Hungary. It's becoming increasingly doubtful he'll have a shot to win, but he's staying optimistic and you just can't count "King David" out.

Rudisha's agent told LetsRun.com in May that the two-time reigning Olympic 800m champ would not be competing in 2021.

Caster Semenya (RSA) and Francine Niyonsaba (BDI)

The defending Olympic 800m champion and runner-up are left without the ability to compete in mid-distance events in Tokyo after World Athletics, then known as the IAAF, implemented new rules in 2019 that require limitations on testosterone levels among competing athletes. The sport federation argued in court that higher levels in female athletes give them an unfair advantage against their competitors. As of now, due to the regulations, Semenya and Niyonsaba can no longer compete in the 400m, 800m and 1500m unless they take action medically to lower their testosterone levels. Semenya has talked about potentially qualifying in the 200m for the Tokyo Games, while Niyonsaba has set her eyes on the 5000m distance to make it to this year's Olympics.

Conseslus Kipruto (KEN)

The defending Olympic 3000m steeplechase champion and two-time reigning 3000m steeplechase world champion pleaded not guilty in November 2020 to "defilement" in his homeland of Kenya, a charge which the Associated Press reports is comparable to statutory rape. The 25-year-old was released on $1,800 cash bail. He faces 20 years in prison if convicted, per the AP, but it's unclear if a verdict, if any, has yet been made.

Salwa Eid Naser (BHR)

The reigning 400m world champion was provisionally suspended by the Athletics Integrity Unit (AIU) in June 2020 for alleged whereabouts failures. The charges were dropped four months later in October 2020 by World Athletics' independent panel. The AIU then submitted an appeal a month later to the Court of Arbitration for Sport (CAS). Those hearing dates were tentatively set for April 2021. It's unclear what will happen.

Liu Hong (CHN)

The defending Olympic 20 km walk champion will be 34 years old come the Tokyo Games and in 2020 admitted she couldn't rule out an early retirement.

Noah Lyles (USA)

The reigning 200m world champion will have a spotlight on him as he enters Tokyo the heavy favorite to replace Usain Bolt at the top of the 200m podium. His 19.50 personal best from July 2019 at Diamond League Lausanne is No. 4 all-time behind Bolt, Bolt's compatriot Yohan Blake and United States sprinting legend Michael Johnson. Lyles, in addition to anchoring the 4x100m relay, could also compete in the individual 100m. While it's not his best event, his 9.86 PR still falls within the top 25 ever run, tied with eight others for No. 17.

Karsten Warholm (NOR), Rai Benjmain (USA)

It's perhaps the most stacked event you will see aside from men's shot put, and its nearly 30-year-old world record held by Team USA's Kevin Young is in grave jeopardy of falling. The men's 400m hurdles will be absolutely electric at the Tokyo Olympics. Norway's Karsten Warholm, USA's Rai Benjamin and Qatar's Abderrahman Samba have all dipped below 47 seconds in the event within the last three years, a feat up until 2018 only ever accomplished by Young. Warholm is the two-time reigning world champion in the event. In Doha, Benjamin took silver and Samba grabbed bronze. This race will be fast.

Joshua Cheptegei (UGA)

The reigning 10,000m world champion broke two major world records in 2020 within two months, taking down both Kenenisa Bekele's 16-year-old 5,000m and 15-year-old 10K marks. He's now the favorite to do what Mo Farah did the past two Olympics: double.

Mondo Duplantis (SWE)

Armand "Mondo" Duplantis followed up a silver at 2019 worlds by breaking the pole vault world record four months later at an indoor meet in Poland, vaulting 6.17m to take down Renaud Lavillenie's six-year-old mark. The next week Duplantis upped his record by a centimeter to 6.18m. Later that year he broke Sergey Bubka's outdoor best of 6.14m.

Brigid Kosgei and Ruth Chepngetich (KEN)

Kenya's Brigid Kosgei has yet to race at an Olympics but has won four marathon majors since fall 2018 and is the world record-holder in the marathon mixed-sex race. Her fellow countrywoman Ruth Chepngetich is the reigning marathon world champion. Chepngetich broke the non-Olympic half-marathon world record in April 2021.

Donavan Brazier (USA)

The reigning 800m world champion has a great shot at becoming the first U.S. man to win Olympic gold in the 800m since Dave Wottle in 1972. His 1:42.34 winning time in Doha is tied for No. 9 all-time. But as the world title-holder he'll have a target on his back. One man who's likely to give Brazier a run for his money is Botswana's Nijel Amos, the silver medalist at the London Games, who ran faster than Brazier did in 2019 clocking 1:41.89.

Other notables:

Mariya Lasitskene (ROC), Steven Gardiner (BAH), Michael Norman (USA), Fred Kerley (USA), Grant Holloway (USA), Michael Norman (USA), Timothy Cheruiyot (KEN), J Ingebrigtsen (NOR), Keni Harrison (USA)

• Keni Harrison, USA, 100m Hurdles: 12.20 (July 22, 2016)
• Anita Wlodarczyk, POL, Hammer: 82.98m (Aug. 28, 2016)
• Beatrice Chepkoech, KEN, Steeple: 8:44.32 (July 20, 2018)
• Eliud Kipchoge, KEN, Marathon: 2:01:39 (Sept. 16, 2018)
• Kevin Mayer, FRA, Decathlon: 9126 (Sept. 16, 2018)
• Team USA, 4x400m Mixed: 3:09.34 (Sept. 29, 2019)
• Dalilah Muhammad, USA, 400mH: 52.16 (Oct. 4, 2019)
• Brigid Kosgei, KEN, Marathon: 2:14:04 (Oct. 13, 2019)
• Mondo Duplantis, SWE, Pole Vault: 6.18m (Feb. 15, 2020)
• Joshua Cheptegei, UGA, 5K: 12:35.36 (Aug. 14, 2020)
• Joshua Cheptegei, UGA, 10K: 26:11.00 (Oct. 7, 2020)
• Letesenbet Gidey, ETH, 5K: 14:06.62 (Oct. 7, 2020)
• Yang Jiayu, CHN, 20km Walk: 1:23:49 (March 20, 2021)

Non-Olympic events:

• Caster Semenya, RSA, 600m: 1:21.77 (Aug. 27, 2017)
• Joyciline Jepkosgei, KEN, 10K road: 29:43 (Sept. 9, 2017)
• Christian Coleman, USA, 60m: 6.34 (Feb. 18, 2018)
• Donavan Brazier, USA, i600m: 1:13.77 (Feb. 24, 2019)
• Liu Hong, CHN, 50km Walk: 3:59:15 (March 9, 2019)
• Sifan Hassan, NED, Mile: 4:12.33 (July 12, 2019)
• Rhonex Kipruot, KEN, 10K road: 26:24 (Jan. 12, 2020)
• Yulimar Rojas, VEN, iTJ: 15.43m (Feb. 21, 2020)
• Joshua Cheptegei, UGA, 5K road: 12:51 (Aug. 14, 2020)
• Kibiwott Kandie, KEN, Half-M: 57:32 (Dec. 6, 2020)
• Hugues Fabrice Zango, BUR, iTJ: 18.07m (Jan. 16, 2021)
• Ryan Crouser, USA, iSP: 22.82m (Jan. 24, 2021)
• Beatrice Chepkoech, KEN, 5K road: 14:43 (Feb. 14, 2021)
• Grant Holloway, USA, 60mH: 7.29 (Feb. 24, 2021)
• Ruth Chepngetich, KEN, Half-M: 1:04:02 (April 4, 2021)