3. WWF SummerSlam 1996
On August 18, 1996 The Undertaker lost a Boiler Room Brawl against his archnemesis Mankind, which was the co-main event of the night.
Taker already had the match won as he made it to the ring first, but then the unthinkable happened and his long time manager and friend Paul Bearer turned Heel and knocked him out with the Urn.
