The strength of warriors past will revive you in battle.
Demongo used to be an enemy of Samurai Jack's when Aku became annoyed at Jack's tactics, and is one of Aku's most powerful servants. Demongo is known as "The Soul Stealer" or "The Soul Collector." While he looks tough, he has a squeaky voice.
In FusionFall, no one is even sure if Demongo survived up to the point when the player arrived in the far Future. Nevertheless, he is within Huntor's Crest in the Darklands in the past. He has strange powers; however, he tells the player during a DexterGuide Mission that Fusion Demongo stole his powers. Demongo seems to know about a super-powerful weapon that could be created from the remains of several of Fuse's enemies that had gone berserk briefly beforehand. He tells the player that spirits of ancient warriors attack Fusion monsters, using their powers to turn them into weapons upon defeat. Demongo seems to have has little contact with any of the heroes, based on his remote location.. Fusion Demongo is apparently one of Fuse's most trusted fusions, since he appears to fight alongside Lord Fuse when the player invades his castle. Demongo also provides information about Aku in Dexter's final Guide Mission. He doesn't say if he is working for Aku, but he says that Aku is near and that he is watching.
Just as Demongo was the right-hand man of Aku, Fusion Demongo is the right-hand man of Fuse.