The Aeon is XX and represents finality as well as true understanding. It symbolizes the rise of the Phoenix from it's ashes, or the understanding acquired during reincarnation. This card is sometimes called the 'evolution' of the Judgement card.
Not many decks have The Aeon, and ones that do have it are void of it's predecessor Judgement. I happen to have a deck that has both. Does anyone know of a deck that has both cards?