Kato (カトー, Katō?) is Marucho Marukura's butler and has helped the Battle Brawlers many times by assisting Marucho and the Battle Brawlers when asked.
Kato is seen wearing a suit and round glasses throughout all four seasons. He has gray hair and a large moustache.
Hal-G once tried to trick the Brawlers by impersonating Kato, but Shun found out when he didn't say "Master Marucho", as Hal-G didn't know how polite Kato was.
Kato also appears many times in Bakugan: New Vestroia, assisting the Brawlers when needed.
Kato appeared in Bakugan: Gundalian Invaders, when it shows Marucho at his home at the table with Ren Krawler.
In Arc 1, he is shown working with Kyosuke Marukura, revealing that he has technological capabilities.
In Arc 2, he is now living in Bakugan City.
Aside from Dan, Shun, and Marucho, he, Miyoko, and Julie Makimoto are the only humans to appear in every season of Bakugan.