Thunder has replaced Sabrewulf as the free character in Microsoft's reboot of the Killer Instinct franchise.
Known as Chief Thunder in the original version of the game, for the purposes of the Xbox One version, he has been renamed as Thunder. As he was before, Thunder is a rather bulky looking American Indian, who wields a tomahawk in each hand.
Due to his story within the game, Thunder is a huge ball of rage, and he's looking to lay down some hurt on anyone who gets in his way.
Killer Instinct, which was developed by Double Helix, has been positioned as a free-to-play experience by Microsoft. This means anyone can download the game and jump in, but they are restricted to using the free character. If they want to expand their roster, they are then required to pay. Up until now, that free character was Sabrewulf.