#4 Bret Hart
Retirement Year: 2000
Retired at: 42
The Best There Is, The Best There Was and The Best There Ever Will Be
The introductory line is the perfect description of Bret Hart, as he was known for his exceptional technique and in-ring abilities. Hart rose to fame in the 80s in WWF (Now WWE), where he helmed The Hart Foundation stable. Following the controversial "Montreal Screwjob" in November 1997, Hart left WWF for WCW.
Hart defended his WCW World Heavyweight Championship against Goldberg at Starrcade 1999. During the match. Goldberg accidentally struck Hart on the head with a brutal kick, severely concussing him. He did return shortly, but in subsequent weeks, he racked up further concussions.
Bret Hart was inactive from in-ring competition since January 2000 and officially retired in October the same year. He did, however, make sporadic appearances as the General Manager of RAW and even headlined SummerSlam 2010 as part of Team WWE.