Punk Rat is one of Benjamin's classmates.
He appeared in Field Trip To Niagara Falls as the main antagonist. He spanked Geronimo on his way into Benjamin's class, causing his glasses to fall off, So when the teacher wrote Field Trip to Niagara Falls thought they were going to the Rodent's Gazette office and agreed, then put on his glasses.
Throughout the book Punk Rat spanks Geronimo.
However, while leaving, the boat forgot Punk Rat and he fell in the water. Geronimo almost instantly jumped in and saved him.
Punk Rat apologizes for the pranks he played, and doesn't bother Geronimo again until they get back to Drew's house and pushes him down the stairs.
He later appeared in A Fabumouse School Adventure, again as the main antagonist. He tells Geronimo that he is not Punk Rat, but his twin brother Modest Mouse, though Geronimo is not fooled.
Punk Rat again plays pranks on him, but claps for him when he finds the missing gecko.