Apsu was Beritra's lover, and ascended around the same time as Tiamat, who was not originally one of the five Dragon Lords. The Lords had decided there would only be five Dragon Lords, and Tiamat was not included. So Tiamat started as a member of Apsu's Protectorate, secretly sowing discontent in the ranks as she worked her way up to becoming Apsu's bodyguard. This position allowed Tiamat to plan Apsu's assassination. Tiamat then replaced Apsu as the fifth Dragon Lord.