Zeo Zagart

Anime
When Tyson first meets Zeo, Zeo saves him from a four on one battle with the Saint Shields. Zeo is just like any other regular blader: inexperienced, slight lack of confidence and is a huge fan of Tyson. He becomes great friends with the Bladebreakers but when he learns that his father, Dr. Zagart, is the man who wants to steal the Bladebreakers' bit beasts, his father reveals the truth to Zeo: he is a robotic duplicate of the real Zeo who died in an accident.

Zeo decides that he will never be able to fit in with other kids and fears that Tyson and the others will reject him for being a robot, so he announces to them that they are now enemies. His father provides him with a powerful bit beast from the stolen rock called Cerberus. Zeo trains hard to control Cerberus and enters the tag team tournament with Gordo as his partner.

When he enters the tournament, he battles Ozuma and beats him. Meanwhile, Kenny discovers a weird anomaly that occurs when Zeo battles. When Zeo battles Kai, he loses and Zeo steals Dranzer from him. Tyson confronts Zeo to try and find the kid he once knew and was friends with, but fails. In the final match he battles Max and steals Draciel and fights Tyson in the tie breaker match. During his battle with Tyson, part of his body short circuits and reveals to everyone that he is a machine. The battle ends with Tyson winning and Dranzer and Draciel being released.

Manga
In the manga, Zeo is actually a boy named Leon who is the younger brother of Zeo. The real Zeo was hit by a truck and died shortly after. He was trained by his father to believe that he was Zeo and battled Tyson to steal Dragoon, but was defeated and realized that he cannot live his life as the shadow of his older brother. Upon his defeat, he and his father leave together to live their true lives.

Beyblade
In the Anime, his original beyblade is called Xeronix (pronounced Zeronix) but was destroyed many times by Sickle Weasel and Clarken, two bit beasts from the stolen rock. After finding about the truth about himself, Cerberus becomes his bit beast with the powerful attack: Chain Storm.

G Revolution
In the final ending of G Revolution (a slide show revealing what happens to characters from other series), Zeo is seen with shorter hair, holding a violin and staring out a window while his Cerberus blade sits on a table.