Sir Aaron is an aura guardian who is referred to as a "legend" in the Kanto region and he made his appearance in Lucario and the Mystery of Mew.
Aaron was born in Cameran Palace where he was a noble and a honored knight to Queen Rin. 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 staff 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 two thousand years later. Later, it seems they were reunited in a spirit world.
- Lucario mistook Ash Ketchum for Sir Aaron when they first met because Ash and Sir Aaron appear to have the same aura. Ash initially thought that it was due to the costume that he wore.
- Sir Aaron has a similar appearance to Riley. Interesting to note that both are aura guardians who have a Lucario for an ally.