Sir Aaron is a legendary hero known as the Hero of the Wave. He was one of the major characters in Lucario and the Mystery of Mew.

Sir Aaron is a knight of Cameran Palace. He is also an Aura Guardian, able to manipulate a type of energy known as Aura, which is why he is called the True Guardian of Aura. He taught Lucario, his student, how to use this energy as well. Because of this, the two become close friends. Lucario, however, still saw their relationship as one of master and servant.

Aaron left the castle to stop a war between two unknown armies before they destroyed his kingdom. He found Lucario, whom he told that he was never going back to the castle. Lucario instantly jumps to the wrong conclusion: Aaron had left the kingdom for dead, and Aaron sealed him in his staff.

Before he died to stop the war, he sent a message to Lucario using a time flower saying he was his friend and that he did not want Lucario to share the same fate he suffered. Aaron said, "Aura is with me," and restored Mew's power by sacrificing himself. Lucario did not know what had happened, and thought Aaron was abandoning the castle instead of saving it.

Ash Ketchum has the same aura as Sir Aaron. Because of this, Lucario first mistook Ash for Aaron. Ash is also able to use the same powers as Aaron when he wears the special gloves that Aaron wore. Coincidentally, Ash dressed up exactly as he did in the tournament.