In 2008, Brock Lesnar arrived in the UFC with a single MMA victory and a mountain of hype behind him. His opponent was former UFC heavyweight champion Frank Mir.
Lesnar opened the fight with a huge takedown, before raining down some ground-and-pound. Referee Steve Mazzagatti then bizarrely stepped in to halt the bout, deducting a point from Lesnar for a blow to the back of Mir's head, and restarted the fight from a standing position. Lesnar initially appeared dominant again, only to find himself in a very crafty kneebar, submitting just 1:30 into the first round.
Lesnar would come back from that loss with a decision over Heath Herring, before successfully winning the UFC Heavyweight Championship against Randy Couture.
Lesnar then got his chance to avenge his UFC debut, defending his belt against Frank Mir at UFC 100.
Ahead of Brock Lesnar's return to MMA after four and a half years away, you can relive that epic showdown below: