Cousin Kevin is a villain in the Who's musical Tommy. He is the 15-to-20-year-old cousin of the title character, whom Tommy's parents hire to baby-sit him. Kevin bullies and mistreats Tommy.
His appearance begins and ends with him playing on the piano, as he does this when Tommy's mother and stepfather are around. It's after they leave and before they return that he takes advantage to Tommy's disability. He succeeds in doing it all behind their backs, and they don't even get suspicious.
Cousin Kevin is played by Paul Nichols in the film. In the musical, he is a baritone.