Aeon is a member of a group that watches over and preserves the flow of time "which Saint Germain is believed to be part of". It is because of Galamoth seeking to take Dracula's throne by erasing the time that he lives in, Aeon goes into action to correct the disturbance to the flow of time by gathering the 13 soul keys and using them to find a chosen warrior to stop Galamoth's messenger, The Time Reaper.
Aeon first appeared in the fighting game Castlevania: Judgment, as the man behind most of the events of the game. Aware of Galamoth's plan to send the Time Reaper to destroy Dracula and change history, Aeon pulls together fighters from different parts of the Castlevania timeline, such as members of the Belmont Clan and their allies as well as Dracula himself and his allies, and puts them into a time rift. He then sets them against each other, and battles them himself, hoping to find the one with the most chance of defeating the Time Reaper. In his story, he defeats all the opponents, therefore requiring him to be the one to face the Time Reaper. Aeon manages to vanquish him, mending the rift in time and returning everyone to their respective eras. With no era of his own to return to, Aeon wanders the ages, observing all that occurs and repairing other rifts in time.
Aeon may be from the same group Saint Germain is a part of, do to the two being the only to time travelers and loveing to talk about the "flow of time"
also Saint Germain once implies that he works for a certain orgainization that travels time wich very well could be the same organization Aeon is with