Leo is the lively and blundering twin brother of Luna. He plays a "Morphtronic" deck , with transforming monsters that have different abilities in attack and defense position, and his key card is Power Tool Dragon. During a life-or-death battle against Aporia, Leo's desire to protect Luna makes him the sixth and final Signer, with the Mark of the Crimson Dragon's Heart. He also comes into possession of the true form of Power Tool Dragon, Life Stream Dragon, which is also a Synchro Tuner monster Yusei can use to summon out his strongest monster, Shooting Quasar Dragon. Leo's original dub name was going to be Luca, this was changed by 4Kids.
Source from Wikipeida