Ultimate

Ultimate is a mysterious figure that appeared on Earth after Sonic and the Avatar defeated Infinite and Eggman, and then suddenly disappeared for a few months. He is the leader of the Ruby Cult and has been trying to achieve a goal of World Domination for roughly half a year. He bears a resemblance to Sonic The Hedgehog and may possibly be him, but he may be a being entirely different than him.

Appearance
Ultimate has 6 long spikes, peach like skin and wears white gloves and dark black shoes with a white stripe and black belt buckle, similar to Sonic's attire but the only difference being the sharper ears and spikes. He wears a wrench-like mask concealing his face and a mysterious gem on his chest that bears resemblance to the Phantom Ruby.

After he unleashes his power, his body and gem unleash a red glow that turns into a corrupt flame-like aura as his body starts to tint a slight red.

Personality
Ultimate is a mysterious cruel, psychotic, selfish, unhinged, and maniacal killer who will do anything to get what he wants similar to Infinite and the rest of the people in his cult. He has stated that he is a former hero who changed to become evil due to his newfound lust for power and blood by the gem he found.

Ultimate is also egotistical and is often bragging about his power and dominance over all beings. He claims to be a "god above mortals" and chokes or tears off the limbs of people who say they are stronger than him.

Ultimate also loves to torture people, he laughs at the screams of the people who are burning to death or are being beaten up by him or his comrades due to his lack of empathy. He kills whoever he gets bored with so he does not waste time from his main goal.

Past
His past is currently unknown, but all that is known is that he was pure good at one point in time, and later became who he is now

Post-Sonic Forces
After Sonic defeated Infinite and Eggman and took back the world, Sonic left to train himself. With Sonic gone for a few months, nobody was able to protect the planet as Shadow and Silver were on a mission taking place on another planet.

Ultimate appeared in Green Hill Zone and proceeded to destroy the landscape. Many animals died and it was not until Tails came and attempted to attack Ultimate, but was grabbed by the leg and thrown to the ground and nearly killed by an energy spear. Tails escaped by luck and Knuckles arrived, but was grabbed by him and thrown into a block of dirt. Ultimate then was about to leave until Eggman punched him with his Death Egg Robot, claiming that he wants to take over the world. Ultimate then got up and kicked the robot and it easily broke apart. After he defeated them, he left and proceeded to destroy the cities surrounding Green Hill, nearly killing the returned Shadow and Silver. Infinite and 3 other people with similar powers joined him and formed the "Ruby Cult". Currently, there are 5 members including Ultimate and Infinite.

Powers and Abilities
Flight - Ultimate can hover above the ground and fly at the speed of light.

Energy Blasts - Ultimate can make energy blasts strong enough to wipe out cities. They can however be blocked or deflected by another force.

Super Strength - Ultimate kicked the Death Egg Robot once and it easily malfunctioned. He also threw a skyscraper on top of a number of people.

Super Speed - Ultimate can run incredibly fast as he easily ran to Station Square in a short amount of time.

Dimensional Travel - Ultimate says that some members of the Ruby Cult are from other dimensions, and said that his gem allows him to do this.

Super Durability - Ultimate was punched by the Death Egg Robot and got back up without any damage.

Object Summoning - Ultimate can summon objects or people and use them for his own interest.

Weakness
Ultimate is not invincible and can be damaged if enough force makes contact with him. Even though he is not fully known, he has stated that he has more weaknesses that cannot be uncovered by just Tails and Knuckles.

Trivia

 * Ultimate's gem can possibly be a Phantom Ruby prototype.