Voltaire Hiwatari (original version: Souichirou Hiwatari, 火渡 宗一郎 Hiwatari Souichirou) is the primary antagonist of the first Beyblade season. He is Kai Hiwatari's grandfather, and also the true mastermind behind Boris, the Demolition Boys, and the BIOVOLT Corporation.
Voltaire is the source of all Kai's misery, forcing him into Beyblading after making Kai's father Susumu Hiwatari chose blading over becoming the heir to Hiwatari Enterprises. He gave Kai a very hard and depressing childhood, making him cold and anti-social like the other Demolition Boys team members.
Upon the Demolition Boys' defeat at the World Championships (and subsequently the undoing of his plot), Voltaire is given away to Interpol by Mr. Dickenson and is never seen again for the rest of the series.