Calypso

They have a big scar from a magic attack he suffered in the past

While he is a supportive colt and can be very nice, he is a very powerful an intimidating unicorn. He can be stern, and hard on ponies. If the situation needs him to be harsh, then he can be very harsh. 

He lives in the hidden school of magic as one of the great professors, in a bedroom built into the teachers part of the dorms