The man who killed WCW was Paul Wight.
Yes, The Big Show is the reason why WCW would begin on its slippery downward slope toward an inescapable demise.
The WWE and its sycophants love to tell the story of Mick Foley and the "butts in seats" comment. They tell this story as though that moment was when fans chose to switch from the fingerpokes of WCW and instead watch the thrilling underdog stories of the WWF.
Yeah, that's a big fucking load of bullshit. Fans were into either show, and there's never been a reliable metric that could indicate that fans chose to switch to the WWF because of the "butts in seats" comment.
Paul Wight was an incredible acquisition for the WWF. Not only was he considered to be a perennial WCW guy at the time, but he was the motherfucking Giant. Fans were now intrigued to see how encounters between this WCW titan would play out against the WWF's main card which now featured some new talent.
Think about the acquisitions that followed for either company.
WCW got a Dustin Runnels who was burned out, and WWF got a Chris Jericho who was starving for the fame he was owed.
Paul Wight didn't just turn the tide of ratings dominance. He was able to provide consistent ratings where the WWF would often have double the numbers of WCW.
Mark my words, pun intended, Paul Wight killed WCW by causing them a slow and painful death after he abruptly left them.