Originally Posted by 2MuchMark

Because George McFly punched him out. He was a bully in 1955, and was a bully in 1855 too, but after George punched him out he changed and became a weenie. This probably got worse over time because George became successful, and Biff didn't. Near the end of BTTF1 George Yells at Biff to give him "2 coats (of wax on his car) instead of 1", and Biff wusses-out. He's no longer a rapist and an asshole.