Clemens Mayer (born September 25, 1985, in Brannenburg) is a German memory sports person. He was World Memory Champion in 2005 and 2006.^[1][2] At the age of 19 years and 10 months, he became the youngest-ever world memory champion in 2005. 12 years later, in 2017, then-18-year- and 11-month-old Mongolian Munkhshur Narmandakh became the youngest champion ever and Mayer lost this record. Narmandakh lost this record to Wei Qinru who won the 2018 world championships at age 14.^[3]

He uses the method of loci. He originally intended to be an Olympic runner, but decided to go into memory sports after watching Gunther Karsten on German television.^[4] Since participating in the South German Memory Championship on 24 June 2007, he did not compete in any championship of memory sports.^[5]