At Blizzcon 2016, two new characters were revealed for Heroes of the Storm. The first was King Varian Wrynn who got a spotlight a few weeks ago. No Blizzard turns to showcase the Lord of the Fire Elementals himself, Ragnaros. This new playable hero has a few unique traits that they breakdown in full during the video… the most notable is an ability to take over an allied or destroyed force, turning him into a raid boss. This isn't a heroic ability but rather a trait, so it will be usable sooner. Ragnaros has to be the biggest melee assassin in the game.
Like Wrynn, Ragnaros comes for the lore of World of Warcraft where he has been a major raid boss twice. First at the heart of Molten Core in one of the earliest raids and then again in Cataclysm as the final boss in the Firelands.