Shadow the Hedgehog

Personality

A loner at heart, Shadow the Hedgehog is an angsty antihero who's motivations tend to shift depending on the situation and his mood. Deep at his core though, Shadow is ultimately committed to helping protect the planet and life as we know it. 

Despite this, he comes across as smug and aggressive, and often antagonizes Sonic and friends. He only maintains a steady friendship with Rouge the Bat and E-123 Omega. His relationship with the main villain Dr Eggman is also complicated, neither seeking his destruction nor committing to being his ally. 

In his early days on the Space Colony ARK, it is thought that Shadow may have had a kinder, more tender personality thanks to his close friendship with Maria Robotnik. Although he has moved on from his past, echoes of this kindness and mercy may still persist in his heart, deep down.

Backstory

50 Years Ago

Space Colony Ark

50 Years before the series aboard the Space Colony Ark, Dr. Eggman's Grandfather, Professor Gerald Robotnik was seeking a means of curing his terminally ill granddaughter, Maria Robotnik. The Government had been seeking a powerful weapon and commissioned Gerald to create it. Seeing the chance as an opportunity to save Maria, Gerald accepted the Government's request. This would be the beginning of "Project: Shadow"

After numerous experiments and research, Gerald eventually reached a dead-end in his pursuits. Gerald would make content with the Black Comet and the alien race dwelling within, the Black Arms. Black Doom, the leader of the Black Arms, assisted Gerald in his research by offering his genetic material in exchange for the seven Chaos Emeralds, fifty years later when the comet would return to Earth.  Using Doom's material, Gerald would eventually complete his research and Shadow the Hedgehog was born. 

Due to the increasing danger of the project as well as questioning Gerald's motives, the government eventually ordered a shutdown of the entire Ark. Soldiers invaded and captured and/or killed multiple researchers, including Maria. Using the last bit of her strength, Maria launched Shadow off the Ark towards the earth before tragically passing on. After the incident, Gerald was captured and forced to continue his development of Shadow under the government's watchful eye on Prison Island; Gerald had learned of Maria's death and swore revenge on humanity, passing his mad aspirations onto Shadow. 

Sonic Adventure 2

In his latest bid for world domination, Dr. Eggman would eventually find his grandfather's diary and the details regarding Project: Shadow and use it for himself. After a raid on Prison Island, Eggman would eventually release Shadow, and feel indebted, decided he would "grant him a wish" and asks to bring more Chaos Emeralds to the Space Colony Ark. Shadow would show Eggman the Eclipse Cannon, a weapon capable of destroying an entire planet, built into the Ark itself and offered it's use as a means of subjugating the planet, which Eggman happily accepted. Unbeknownst to both, they were being eavesdrop by one Rouge the Bat and reluctantly accepted her her help. 

After numerous conflicts with Sonic, Shadow would eventually reveal that he was working on behalf of the late Professor Gerald to activate a program aboard the Ark that would turn the station into a bomb charged by the Chaos Emeralds and destroy the planet, all as a means of revenge for the events of 50 years ago. Amy Rose would eventually find Shadow alone in the Ark and try to convince him to assist the other heroes in stopping the Ark. This conversation triggered a latent memory in Shadow that Maria had wanted him to act as a protector of the planet and fight on its behalf for the sake of others. With renewed purpose, Shadow would go and join Sonic and stopping the Ark from colliding with the planet, and sacrificing himself in the promise.

Sonic Heroes

Survived? Release; Amnesia.

Is he an Android?

Shadow the Hedgehog

Return of Black Doom; 

Destruction of Central City.

Recovered Memories;

Defeats Black Arms; Destroy Black Comet.

Finally moves on from the past.

Hidden Palace Mural Origin Theory 

[Should address that this was never confirmed and that this is just a persisting fandom headcanon, but include it here just in case]

Abilities

Shadow is among the most powerful beings in the series, even able to match the speed and abilities of Sonic the Hedgehog himself thanks to his air shoes and mastery over "Chaos Control." 

Like Sonic, Shadow can curl into a ball and use the roll jump, spin dash, homing attack, somersault, ring dash and boost. However, Shadow often relies on his strength and Chaos Powers to fight enemies, making him the most versatile fighter in the main cast. 

Chaos Powers 

While he's notably similar to Sonic in regards to his abilities, it's his Chaos Powers that act as his signature method of combat and mobility.

Chaos Control allows Shadow to warp time and space, allowing him to teleport and freeze the flow of time. This move uniquely requires a Chaos Emerald to be used, though he has utilized a more limited form of Chaos Control without one in the past.

Chaos Spear is a projectile move made of pure energy that zeroes in at targets from a distance.

Chaos Blast is Shadow's most powerful move, using pent up energy to create a massive explosion, leaving destruction in it's wake. 

Chaos Boost is a temporary enhancement of Shadow's abilities, making him stronger and faster

Chaos Snap is a short-range teleportation move that aids in combat. 

Super Shadow

Like Sonic and Silver, Shadow is also capable of using the seven Chaos Emeralds to transform into "Super Shadow." In addition to the standards buffs such as invincibility and enhanced speed, Shadow's other Chaos Powers are augmented to be more powerful. Like everyone else with a Super transformation, this form is limited and requires rings. 

Inhibitor Rings