Superdude was a character played by Kenan Thompson in the first five seasons of All That. As the name and outfit suggest, he was a parody of DC Comics' Superman. He is the alter ego of Mark Cant, a student at Durmont Junior High School. His one weakness is that he is lactose-intolerant, and thus is weakened by dairy products.
Each Superdude sketch usually began with Mark and his girlfriend Penny Lane being harassed by bullies, resulting in Mark running off to transform into Superdude and get rid of the harassers. One of Superdude's dairy-themed villains would then show up and immobilize him with a dairy product, but Superdude's friends would always come to his aid, allowing him to defeat the villain.