From Bulbapedia, the community-driven Pokémon encyclopedia.
Sir Aaron (Japanese: アーロン様 Āron-sama) 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. His Japanese voice actor is 山寺宏一 Koichi Yamadera and his English voice actor is Jason Griffith.
Aaron is able to manipulate a type of energy known as aura, which is why he is called the Hero of the Wave. He taught Lucario, his student, how to use this energy as well. Because of this, the two become close friends.
Aaron risked his life to stop a war. Before he died, 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 shared. Aaron said, "The wave is in me," and restored Mew's power by sacrficing 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.
Sir Aaron owned the following Pokémon: