Whom is the oldest champion in LoL?

Aurelion Sol is my guess. According to lore he is the equivalent of the big bang event, having created Runeterra

Oh, I thought you were talking about oldest in terms of chronologically who was created first. In that case, I think Annie was the first champion the Rioters designed, I know that there were 6 champions when the alpha was released though. In the case of who is the oldest in the lore, Aurelion Sol for sure, considering he created the universe.

zilean? wouldn't he be considered ageless making him the youngest and oldest? Brands essence is likely ageless too seeing that he is a god. Maybe disqualify the beings that can exist outside of time.

sol,bard,kindred