#10 Rey Mysterio
The master of the “619” has been a fan favorite throughout his career; and he was a true personification of an underdog in the WWE due to his size. But, what he lacked in size, he made up in tenacity and agility and became a 3-time World Champion in the process.
However, frequent injuries and lack of direction in his character increased his frustration with the WWE. He decided not to renew his contract with the company and signed up with AAA for the first time since 1995.
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However, Rey had to leave AAA in February 2016, almost a year after leaving WWE, due to financial disputes. He has since then been wrestling on the independent circuit and Lucha Underground. Had Rey shown a some amount of patience, WWE may have inserted him into a meaningful feud as he was undisputedly a crowd puller and a big name.