Specialty: Staff, Water and Sun Magic
Tiberius can be found in the Divine Tower during the Maximus Chase Quest. After Maximus declares he's landing on the roof, and your conversation ends, talk to Tiberius a second time, and he'll offer to join you. You'll need Tiberius to complete the Shinon Secret.
Tiberius is actually a very good healer. He specializes in both Water and Sun Magic and is pretty decent with a staff. Don't expect him to do tons of damage, he is a magician after all.