Gelios (ゲリュオス, Geryuosu) and John Owen (ジョン・オーエン, Jon Ōen) or John Owen, are an ancient Mamodo team who confronted Zatch Bell and Kiyo Takamine and Tia and Megumi Oumi, along with Alm. Gelios's spells usually involve Body Enhancement Magic but in the anime, he was also shown with a water spell. John Owen is a baseball player, which mind is brainwashed for Zofis. John's Japanese voice is provided by Keijin Okuda; English voice is provided for Kyle Hebert.
Gelios is at the water reservatory, along with Alm, protecting it from any intruder, and then they meet Kanchomé, who distracts them into a trap. After this, Ganz appears and he's taken for Kanchomé and Folgore (after Ponygon follow them). However, Alm and Gelios wake up and start attacking Zatch, Kiyo, Tia and Megumi. After using Akuru on them, Kiyo makes a plan to escape from Gelios' attack. The two ancient mamodo then follow they into a more lower arena. There Zatch starts using a strategy to burn their books: Don't hit the bookkeepers. Later, they use their strongest spells: Egudorisu Neshiruga, Baou Zakeruga, Gigano Dioderuku and Ma Seushirudo. While those attacks cancel each other, Megumi gets Alm and Gelios' books. Seeing that there's no chance of winning, Alm tells to them everything that he knows, and fades along with Gelios.
In the manga Gelios's spirit is seen assisting Zatch along with the other Mamodo's in his final attack against Clear Note, After Zatch became king he was revived along with the other Mamodos and is shown to be in the same grade as Laila, Pamoon, Hyde, Reycom, Pokkerio, and Paramakion.
Gelios is a giant snake-like mamodo whose face is reminiscent of a court jester. John Owen appears to be a baseball player.