Dathan James Ritzenhein (born December 30, 1982) is a retired American long-distance runner, and current head coach of the On Athletics Club (OAC).

Formerly a Nike athlete for the majority of his professional career, Dathan joined the Hansons-Brooks Distance Project team in 2017.

He signed with the Swiss shoe brand On shortly thereafter in June 2020 and currently acts as the coach for the OAC in Boulder, Colorado.

He won back-to-back regional (Midwest) and national titles in the Foot Locker high school championship races in the fall of 1999 and 2000.

His final cross country race in high school was at the IAAF junior world cross-country championships in Ostend, Belgium where he won a bronze medal.

[5] Ritzenhein began to attend the University of Colorado at Boulder in the fall of 2001 to major in history and compete intercollegiately in cross country and track.

The following spring he competed in the 5000 m race at the NCAA Track and Field Outdoor Championships, finishing again in fourth place with a 14:01.02.

Ritzenhein concluded his collegiate season by placing second to Robert Cheseret of Arizona in the 5000 m at the NCAA Outdoor Track and Field Championships.

Ritzenhein harbored hopes of competing in the Olympic Games at the end of the summer in Athens, but shortly after the NCAA meet he developed a stress fracture in his foot.

Before the World Cross Country Championships expectations were high and some prognosticators even predicted a top 10 finish, but Ritzenhein faded after going out with the leaders and ended up placing 62nd.

He qualified for the team but appeared to be hurting badly after the race, leading some to question his fitness heading into the IAAF World Cross-Country Championships April 1–2.

[10] Just eleven days later at the Weltklasse Meeting in Zurich, Switzerland, Ritzenhein placed 3rd in the 5,000 metres, setting a new American record with a time of 12:56.27.

He became just the third American to run under 13 minutes in the 5,000, as well as the third fastest non-African of all time in that event behind Dieter Baumann and Craig Mottram.

[17] A fast finish at the 2012 Chicago Marathon saw him move up into ninth place, the fastest non-African runner, and set a new personal record of 2:07:47 hours.

"[21] On May 9, 2014, Ritzenhein announced that he would leave the Nike Oregon Project to move closer to his hometown of Grand Rapids, Michigan.

[24][25][26] Dathan plans to continue coaching; he hopes to attract talent to Grand Valley State University in Michigan.

[27] Ritzenhein was named the head coach of the newly formed On Athletics Club (based in Boulder, Colorado) in August 2020.

[28] Since the club's formation, Ritzenhein's athletes have clinched Olympic medals (Hellen Obiri & Yared Nuguse) and World Athletics Indoor Championships medals (Geordie Beamish & Yared Nuguse), won three World Marathon Majors (Hellen Obiri), and amassed numerous national records and titles.

[29] Oliver Hoare whom he coaches at the On Athletics Club, regularly uses his quintessential Australian humour to perform impressions of Dathan on the CoffeeClub Podcast.