As quoted from Bill Watterson:

"Moe is every jerk I've ever known. He's big, dumb, ugly and cruel. I remember school being full of idiots like Moe. I think they spawn on damp locker room floors."

As quoted from Me:

Moe is like the serious person's way of confronting the violence found in schools, but with a twist of Calvin's famous humour. He bugs Calvin at school but Calvin usually gets back at Moe by getting him to say something stupid or else making an intelligent insult which just flies right over Moe's head.