Simon Belmont originates from the first Castlevania game. He is considered to be the most iconic out of all Castlevania protagonists, and his fame is great enough to take him to plenty of games outside of the series, including Super Smash Bros. He may not be the first Belmont, chronologically speaking, but he is the one that made the Belmont name known.
Castlevania: Waltz of Remembrance 