#1 Eric Bischoff
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Eric Bischoff is easily the most surprising name to ever sign with WWE. No, he wasn't a wrestler that didn't fit the WWE bill or a top performer from another company who never needed WWE.
Eric Bischoff was the Executive Producer and later President of WCW and during the Monday Night War, Eric made it know, weekly, that it was his goal to put the WWE out of business. Eric would bring the real-life rivalry of he and Vince McMahon to TV, often taking major shots at WWE and going as far as to give away taped results of shows.
WWE finally got one over on Eric in 1998 when D-Generation X 'Invaded' an episode of Nitro. However, Eric responded, ingeniously, by taking the attention off of DX and challenging Vince to a match at WCW Slamboree that year. When Vince elected not to show up, Eric had embarrassed him even more and declared victory.
On top of all that, Eric made WCW so popular by personally offering contracts to all of Vince's current, former and top performers, successfully signing the likes of Hulk Hogan, Scott Hall, Kevin Nash, Randy Savage, Lex Luger, Bret Hart and many more. Eric did enough to Vince to make Vince make sure that Eric would never see work in the wrestling business again, following the death of WCW.
However, what we shockingly got instead was Vince putting his personal differences aside and recognizing Eric's fantastic TV character talents, and offering him a TV role as the General Manager of WWE RAW in 2002. Eric accepted, and remained in that position until late 2005, becoming the best TV General Manager in the history of WWE.