Andre Ward, Ann Wolfe, Marian Trimiar and ring physician Margaret Goodman are also among the inductees. Boxers Davey Moore and Jackie Tonawanda, cut man Freddie Brown, trainer Jackie McCoy, journalist George Kimball and television executive Jay Larkin will be inducted posthumously.
Mayweather ended his boxing career at 50-0, with his last fight being a TKO victory over Conor McGregor. He's set to return to the ring for an exhibition match against YouTuber Logan Paul in February.
Ali, the daughter of Muhammad Ali, went 24-0 in her own boxing career from 1999 to 2007.
Klitschko was a heavyweight champion for the better part of a half-decade, running the heavyweight division during an undefeated run that lasted from September 2005 through November 2015. He retired at 64-5, losing back-to-back matches to Tyson Fury and then Anthony Joshua.
The 2021 Hall of Fame class will be inducted at the same time as the 2020 Hall of Famers, a group highlighted by Bernard Hopkins, Juan Manuel Marquez and Shane Mosley. Mayweather defeated Marquez in 2009 and Mosley in 2010.
The ceremony will take place June 13, 2021.