Leon is a merchant in the Savina marketplace. You don't buy anything off him, but he has a part of the main story of the game.

When you first talk to him, you notice a weird crystal on the table that he is selling. Shortly afterwards it starts to glow which confuses Leon who has never seen it glow before. You then convince Leon to play for the crystal in a round of shell game. If you lose, he gets your sword.

But you win and get the crystal which turns out to be a shard of the powerful artifact the Tear of Neriah.