Mister Sinister was the Baron of Bar Sinister, one of the domains of Battleworld. He and King Hyperion were working against the House Braddock of Higher Avalon, another domain of Battleworld, when the God Emperor Doom's force, the Thor Corps brought him to the Castle Doom in Doomgard. Sinister was accused by Baron Braddock of Higher Avalon, and clashed with Baron Braddock's brother, Brian Braddock, in single combat. Sinister was near victory when God Emperor Doom stopped the match.
When Iron Thor was found dead in Utopolis, King Hyperion sought the counsel of Baron Sinister to help discern whom the murder might be. Sinister informed him that it was likely a traitor within his own ranks, someone wishing to personally do him harm. Sinister also possessed Fare-Devil as a chef and used Collektra to hunt exotic beasts for him.
Captain Marvel one of the survivors from Earth-616 was captured by Baron Sinister after Sheriff Strange scattered the survivors across the Battleworld. They were later seen together after Sinister finished his meeting with God Doom who gathered his Barons to discuss the threat of the Prophet who was gaining support across the Battleworld. Captain Marvel apparently under control of Sinister helped Sinister decide to betray God Doom. Sinister and Captain Marvel attacked the other Barons instead of the Prophet's army. During the battle, Sinister's head is removed and brought before Apocalypse where they argued before the Thors arrived to fight as they too had betrayed God Doom. The Maestro and his Worldbreakers also joined the battle against God Doom and separated Sinister and Apocalypse. Sinister was apparently killed as Meastro's ship crashes down on him, as he was just a head and couldn't flee.
- 7 appearance(s) of Nathaniel Essex (Earth-21919)
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