The Phantom Renegade is Henry's alter ego. He always comes durring the night, but nobody knows exactly when. He steals the medals of Medabots, and is especially after rare ones. He becomes a good guy later on in the series.
Hikaru Agata was the world robattle champion 8 years ago. He is the same one who caused his Medabot, Metabee (yup, Ikki's Metabee.), to set fire on the world Robattle stadium in a Robattle and cause chaos among all medabots around the world for ten days (the ten days of darkness, revealed by Tom of Team U.S.A.).
This robattle's records vanished, even the reports were nowhere to be found (the forgotten robattle). Hikaru Agata, too, disappered and became the Henry that Ikki knew, and he sold his old medabot to Ikki.
He works with Dr. Aki in search of rare medals to protect as The Phantom Renegade. But the Phantom renegade was a known criminal, so he closely guarded his secret identity. In the World Robattle Championship, a mysterious "Space Medafighter X" turn up and is later known to be the number one medafighter in Japan, which, they find out at their battle with Mega-Emperor, and the robattle between Team USA and Team Japan, was the Phantom Renegade.