Sperg is a bully in The Grim Adventures of Billy and Mandy. His first appearance was as the main antagonist in the episode "Billy and the Bully".
There are countless episodes where he beats up and humiliates Billy , Irwin, Pud'n and other dim kids but one of his worst acts was cannibalising Pud'n when they were stranded in the desert just because he was a little hungry. Being the sadistic psycho that he is this was just one of the many excuses of wanting to harm for his profit the dorky kid.
Despite his strength, he is extremely terrified of Mandy.