Nessus was a mercenary centaur who usually associated himself with Hades.
Disney vs Non-Disney Villains War - Part Two
Nessus plays a minimal role in the second war, acting as one of Hades's field operatives. The centaur encounters the demon Aku, who is planning to kill him. Overconfident as ever, Nessus laughs at the very prospect of losing to Aku, only for Aku to fire lasers at him. The shot is accurate; Nessus is sent careening into a waterfall. Nessus recovers and blindly charges at Aku, while the demon transforms into a strange gorilla-hybrid. The hybrid launches Nessus into the air; as soon as the centaur lands, his horseshoes fall on his head, knocking him unconscious. As Nessus is in the water at the time of his being knocked out and because Aku leaves him there, it is safe to assume Nessus drowns.
Disney Villains War
During the Second Villains War, Nessus was again recruited by Hades, this time as a soldier.
He participated in the Invasion of the Forbidden Mountains, though most of his role in the battle is unknown. He fought for Hades, defending the Forbidden Mountain from soldiers sent by Doctor Facilier and Narissa to conquer it. When the sorcerer named Mozenrath, who was fighting for the enemy faction, fled from the battle, Nessus was sent by Hades to kill him. More than eager to finish him off, Nessus ambushed Mozenrath near the bottom of a waterfall, confident that he could defeat him. However, Mozenrath effortlessly dealt with the centaur using his magic, tossing him into the air and injuring him with his own horseshoes, and finishing him off using a magic blast. Nessus' defeat angered Hades.
It is unknown whether Nessus was killed by Mozenrath's magic blast, or if he was merely knocked out.
Personality and Traits
Nessus was marked by his arrogance and preference of brute force to carry out his goals. He was apparently loyal to Hades, and was more than eager to carry out his orders to the letter. However, his sadistic and brutal personality may have been the reason for his loyalty to Hades. Nessus was not very intelligent, usually charging into a fight without a strategy or plan. This was demonstrated by his attempt to attack Rasputin, despite knowing that he was a magic user and that his only means of disabling his magic was taken. This was a personal flaw which usually led to his defeat.
Powers and Abilities
Nessus was a brutal and skilled fighter who relied on brute force and power to defeat his enemies. Though usually having a disadvantage against magic users, he still proves himself to be a formidable fighter. He was very strong physically, an asset which usually assisted him in the fights which he participated in. Nessus also demonstrated resourcefulness, using a magic rope which could absorb the powers of a magic user in his attempt to kill the Emperor of The Night. And if it weren't for Rasputin's intervention, Nessus would have brought about the end of the powerful emperor, and possibly the Nightmare King as well.
Hades was Nessus' master whom he was very loyal to. Though it is likely that Nessus served Hades out of his love for fighting, he was always more than eager to follow Hades' orders to the letter (or at least the orders which allowed him the opportunity to fight an opponent) and was regarded by the Lord of the Underworld as his most skilled assassin.