Trevor Belmont is Simon's great grandfather in the Castlevania series.

Castlevania II

Trevor made his first appearance in Castlevania II. He has a weapon called the Vampire Hunter. Players can play as him in this game.

Castlevania: Curse of Darkness

Trevor was a secret character and he can only be unlocked at the name in the fashion, @TREVOR.

Other media

Trevor Belmont was a mentioned only character in the Captain N Series. The reason for this was because he was alread deceased by this time and at some point in the past so he was seen buried on the show. This fact is significant becasue he was the only Captain N character to actually be buried in a cemetary. If you look closely, you can see the words reading "TREVOR BELMONT". His tombstone appeared in Return to Castlevania.