Inferno is a playable character in Soulcalibur 6.
The original Soulcalibur boss was revealed by publisher Bandai Namco with the gameplay video, below. The "Hellfire of Despair" uses Soul Edge, the demonic weapon at the heart of the fighting game series. Inferno's fighting style is "whatever the fighting style of those under his control". In previous Soulcalibur games, Inferno used a mimic ability to copy the moveset of his opponent, in combination with a few unique moves of his own. It sounds like he works the same in Soulcalibur 6.
It's worth noting Bandai Namco states Inferno cannot be used in online multiplayer. Inferno was always overpowered, and given his mimic ability, perhaps Bandai Namco thought he'd end up dominating competitive play. Still, you'll be able to use Inferno in local multiplayer.