I thought it would be interesting to make a list of the people who performed at the highest levels in other combat sports before or after getting into MMA. I want this to really be a list of legitimate champions--no Karo for judo or Sakara for boxing and no sports with disputed pedigrees and championship credentials. I'm not going to do a whole lot of research, so hopefully you guys can supplement the names in these categories:
BJJ/Submission wrestling (ADCC absolute or superfight champions only)
Judo (Olympic gold medalists only)
Wrestling(Olympic gold medalists only)
Kickboxing (K-1 GP champs or Thai stadium champs only)
Boxing (IBF, WBA, WBC or WBO world champs only)
(Mohammed Ali and Tommy Morrison under very restricted MMA rules)
I am fairly certain Goodidge won a K-1 GP. Can't remember which one though.
EDIT: I looked it up and it wasn't a world GP, just a Hawaii one
Also Cung Lee was a San Shou champ I beleive. I am not sure if that counts or not
Melvin Manhoef immediately came to mind when I saw the kickboxers, but I don't know if he ever won any K-1 titles.
well i know this is obvious but...:
Fedor- multiple time World Combat Sambo Champion and Russian Combat Sambo Champion
Aleks- two-time Russian national Sambo champion and two-time world Sambo champion in the absolute divisions
Arlovski (on the edge of putting him on the list)- Junior World Sambo Champion, as well as a silver medalist in the World Sambo Championship and World Sambo Cup.
Also, Jacare was the 2004 and 2005 Openweight World Jiu-Jitsu Champion.
and although he didn't technically win any OW championships, he came pretty damn close which is amazing for someone his size; so honorable mention to Marcelo Garcia.
A little arbitrary and maybe a bit snobby, but I did not want to include sports like San Shou, karate, sambo, etc. where there is not an Olympic track or a well-established promotion which forces champions and contenders to meet. I don't think the world championships in sports like that carry as much weight, but that's solely a personal opinion.