Crabbe is large, has gorilla-like arms, and wears a pudding bowl-style haircut. He is very mean and very stupid, which makes him little more than a "follower" of Malfoy. In Harry Potter and the Order of the Phoenix, he joined the Inquisitorial Squad. In the third movie, Harry, under the invisibility cloak, pantses Crabbe, who is unable to pull back up his pant and is forced to hop away.
Crabbe is a lot like Dudley Dursley, being fat, stupid, and bullying. Hermione tricks him and Goyle into eating cakes spiked with sleeping potion.
He seems unable to make up his own mind or to see things his own way; he is generally told what to do. Nonetheless he is depicted as more intelligent than Goyle and in the Half-Blood Prince he seems to quarrel with Malfoy for the first time. In the same book, he and Goyle are turned into girls via Polyjuice Potion.
His and Goyle's personalities are sometimes questioned by some readers, as Slytherins are typically described as "cunning". However, both are likely power-hungry, or simply do not fit into the other houses as well as they fit into Slytherin.
