#1 Brock Lesnar walked out of WWE and sued the comp
Brock Lensar made his debut for WWE in 2002. After his underwhelming match against Goldberg at WrestleMania XX, Lesnar decided to leave the company to pursue a career in the NFL. In a 2005 article on PWTorch.com, it went into details about Lesnar's departure from WWE:
"Lesnar signed a talent contract extension with WWE in 2003 that took effect July 1, 2003, and was set to last until June 30, 2010. Less than a year later, with a desire to attempt to play in the NFL, he asked to get out of his contract. WWE agreed to let him out of his contract, but only if he signed a non-compete clause."
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The no-compete meant that Lesnar couldn't compete in a wrestling or ultimate fighting match until the contract expired. Lesnar agreed to sign the deal because at that point he believed he was going to have a successful career in the NFL but, unfortunately, once the NFL plan didn't work out, Lesnar ended up suing WWE because he needed to make a living and he wasn't allowed to compete in any wrestling promotion.
In 2006, WWE and Lesnar reached an agreement to settle the lawsuit and Lesnar was free to do what he wanted to do. He joined New Japan Pro Wrestling and then in 2007 he started his MMA career and as they say, the rest is history. You won't hear WWE mention the fact that Lesnar not only chose to walk out of the company, but he also sued them. In the end, Lesnar returned to WWE and is making millions even though he is a part-timer.