#1 Bret Hart (Released by WWE in 1997)
Yes, Bret Hart eventually returned to WWE, but the situation leading up to his departure in 1997 is a vital part of pro wrestling history. At a time when kayfabe was still very much prevalent, the incident, dubbed the "'Montreal Screwjob," became infamous.
Hart made up his mind about leaving WWE shortly before Survivor Series 1997. But he presented two conditions to Vince McMahon, as he said he wouldn't drop his WWE Championship in Canada, his home country. He made it clear that he would not lose the title to Shawn Michaels.
Heading into Survivor Series, it was decided that Hart would retain his title and forfeit it at a later date. But McMahon and WWE planned a screwy finish where the referee called for the bell, even though Hart did not not tap out to the Sharpshooter locked in by Michaels.
It was a controversial ending, and Hart was visibly angered by this outcome. He left the company on a very bitter note, but he eventually made his return in 2010. Years after the Montreal Screwjob, Hart buried the hatchet with McMahon, and he has made a few appearances on WWE programming in recent years.