A Phoenix. The Duke of Threewalls.
Allistar came to Dragaera City at the beginning of the reign of Tortaalik with his sister Illista. It was Allistar's intention to influence the politics of the court, particularly the fate of Kathana e'Marish'Chala, to gain favor with the Emperor.
When his efforts were foiled, Allistar and his sister were banished to Elde Island. He presumably died sometime before Zerika's trip to the Paths of the Dead to retrieve the Orb. According to Paarfi, around this time the gods reflected on the impossibility of the House of the Phoenix regenerating from the two remaining female specimens.
In fact, when Illista later recounts her exile to Elde Island and her request for sanctuary with its King, she doesn't appear to recall Allistar's even having been present. Perhaps he died on the way there.