Sir Aaron is a "legend" in the Kanto region.
He was born in Cameran Palace and was a noble and honored knight. When two armies were about to fight, Sir Aaron went to the Tree of Beginning and sacrificed himself to save the kingdom. He has the ability to use aura, along with his student and friend Lucario, whom he traveled with.
Sir Aaron sealed Lucario inside his scepter so Lucario wouldn't sacrifice himself to save the Cameran Palace, and that he could live in a time of peace. Ironically, Lucario ended up meeting the same fate when he gave his life energy to save Mew and the Tree of Beginning one thousand years later. Later it seems they were reunited in a spirit world.
- Lucario mistook Ash for Sir Aaron when they first met because Ash and Sir Aaron appear to have the same aura.
- Sir Aaron has a similar appearance to Riley.