Harley Keiner is the leader of the bullies at John Adams High. His oldest lackey is Frankie and his newest one is Joey. He tried to recruit Shawn, but was thwarted by Cory. In Back 2 School, Cory tried to make friends with him as a way to gain instant popularity, but Harley instead chose to target Cory. Because of a prank he played on Cory, he refers to him as "baboon" (Johnny Baboon).
The episode Sister Theresa reveals Harley's family life and a more sympathetic side to the bully. He has a sister, Theresa Keiner, whom he truly cares for. Apparently when Theresa was eight, their father ditched Theresa at a Phillies game to run off with another woman. Harley went out of his way to get to the Phillies game and escort her home.