Leon is one of Cazador's spawn and Astarion's "siblings". Before he was a slave, he was a Sorcerer, and is also the father of Victoria[1].
Cazador forced Leon to bring Victoria to the palace, and ever since he has tried to keep the position of Favoured Spawn so they could stay together in the 'favoured spawn' bedchamber. He organised an escape for Victoria, but she was later brought back to the palace where she was killed by Dalyria.
Leon and Victoria's belongings can be found in the favoured spawn bedchamber, including Leon's diary and Victoria's Stuffed Owlbear Toy.
Involvement
During act three, Leon may be encountered at camp with three other vampire spawn. They will arrive in the dead of night, seeking to bring Astarion home. He and his fellow spawn can be persuaded that Astarion will help them, but regardless they will be compelled to attack. Failing to defeat them before Astarion reaches one hit point will allow them to take him back to the Szarr Palace. Astarion will then be found in the kennels with Godey.
He will later be found at Cazador's Dungeon with the other spawns, suspended and awaiting Cazador's ritual to finish. Like the other spawn, he can be spared or killed after the ritual, or allowed to be consumed as one of the ritual's sacrifices.