#2 Daniel Bryan
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Bryan came in as a member of the rowdy group from NXT's first season, Nexus. The group's infamous attack on Monday Night Raw in 2010 led to Bryan being let go for "being too violent". He came back at Summerslam to join John Cena's Team WWE, which eventually defeated The Nexus in the main event of the night.
Also read: 4 incredible sacrifices Vince McMahon made for WWE
Soon, Bryan was elevated to the main event, and won the WWE Title by defeating Cena at Summerslam 2013. A shocking heel turn by Triple H led to Randy Orton cashing in his MITB contract on Bryan and winning the belt. This resulted in the Yes Movement gaining huge coverage and getting mainstream attention, eventually leading to Bryan defeating Orton and Batista in the main event of WrestleMania 30 to become the champion. The storyline is regarded by many as possibly the greatest underdog story WWE has ever come up with.