Abu (sometimes called Apu) was a highly intelligent monkey who lived in the Swamps of Ichtaka. He traveled with the then un-named Ätlän-tã Fælcons until they traveled forward in time from the period of the reign of House Vidalis when he, presumably, failed to make it through the portal. His whereabouts are, however, officially unknown. In an episode I don't remember, before The Battle Above the Abyss, Michael says that Abu did in fact, make it out of the portal, and is missing. We shall see if this is ever brought up again.
In Episode 160 - Monkier Business, the party saved a group of monkeys (to which Bananas Foster belonged) that claimed to know Abu.