Leroy Jenkins, a killer of the most callous kind, has been on the Most Wanted List for literally decades, until, in the wake of "Last Night Gus", the boys discover that they have stumbled across one of his victims, and proof of his whereabouts. Unfortunately, Leroy has an accomplice, and step-daughter, who is largely responsible for the gang's gaping holes in their recollection of the previous evening, and she lures Gus back to her place, where 'Daddy' is waiting with a gun to reacquire the evidence that could put him away. Gus, however, is in a stupor which renders him oblivious to his peril, and eventually takes out the gun-wielding maniac - with a snack bowl.
The character is played by Peter Kent. He is presumably named for the Internet meme Leeroy Jenkins.