Voltar's past is shrouded in mystery. Rumor has it he once was a researcher at a star-encapsulating power station. The station made intergalactic headlines when it exploded around 500 years ago, sending off all kinds of strange, unseen radiation into space. In this explosion, the AI core of the Zero’s was destroyed, bringing an abrupt end to the First AI War. Although peace was maintained for some centuries, the war eventually returned. Some think that war was just too profitable, and suspect that weapon manufacturers had a hand in the construction of a new AI core for the Zero's.
The explosion at the power station destroyed almost every part of Voltar's body, leaving only his brilliant brain intact. This brain was carefully placed inside a Braintank by salvagers. Through the years, and with help of his loyal robot drones, he made some nifty modifications to his braintank that enabled him to participate in the newly erupted Robot Wars.
No-one knows Voltar's true motives for participating in the war as a mercenary, but what can be assured is that he's a mastermind with unmatched psychotechnic powers and an arsenal of armed robots that do his every bidding.
Source: The Developer Website.