WWF eventually surpassed its arch-rival WCW. With its business steadily declining and a corporate takeover of its parent company (Time Warner) by America Online, WCW was put up for sale and purchased by Vince McMahon in 2001, once again making WWF the single-largest wrestling company in North America. Bret Hart's entry into WCW had been hailed at the time as a major coup for the company, but it subsequently failed to utilize his popular appeal. Hart's active wrestling career ended in 2000 after he suffered a serious concussion during a match with Goldberg. After dropping the WWF title to Austin at WrestleMania XIV in 1998, Michaels was forced into retirement for four years due to a serious back injury. After a long period of rehabilitation, Michaels returned to the ring in 2002 at SummerSlam, and eventually retired in 2010 at WrestleMania XXVI, losing a Streak vs. Career match to The Undertaker in the main event, but came out of retirement for one match eight years later at Crown Jewel in 2018.