Shadow is an artifical life form created by the brilliant scientist named Gerald Robotnik. He is considered to be humanities first step into discovering the secrets of immortality, nicknaming him "The Ultimate Lifeform". Shadow is immune to aging, which means he can live in his youthful state forever. Shadow is also considered to be a cure for Gerald Robotnik's grandaughter Maria Robotnik who has developed NIDS (Nuero Immune Deficiency Syndrome).
Due to his creation and suspiscion behind Gerald Robotnik's motives, G.U.N moved in to investigate. During the investigation, all experiments were put on hold, all scientist on Space Colony Ark were arrested, and those who attempted to escape would be shot on site. Shadow and Maria made their escape to the evacuation room, to get into the emergency launch pods and head to earth, unfortunately getting Maria shot in the back in the process. Maria sent Shadow to earth with her last dying words, telling him to give the people of earth a chance to be happy. Maria died on the Space Colony ARK.
50 Years LaterEdit
Shadow's lauch pod landed on earth with him inside, which was eventually uncovered by G.U.N. Shadow was taken back to G.U.N's island base where he was contained in suspended animation. Professor Gerald could finish the project he started so G.U.N could one day use Shadow when they needed him. The Professor secretly began his planning for revenge against the earth for what they took away from him.
To realize his revenge the Eclipse Cannon aboard the Ark must be activated by the Chaos Emeralds, and then his revenge would be realized. Then behind G.U.N's back, he implanted his revenge plan in Shadow's brain, so if one day he were awakened, his revenge would be exacted. Professor Gerald was executed later on, and Shadow would remain in suspended animation for 50 years. Shadow was finally awoken by Gerald's grandson, Dr. Ivo (Eggman) Robotnik.
He mistook Shadow for Sonic the Hedgehog, at first but the two of them became partners to find the seven Chaos Emeralds and acheive world domination. The Duo would soon be joined by spy/jewel theif Rouge the Bat who is secretly on an undercover mission to uncover the secrets of Project Shadow. The Trio would eventually go on to collect the chaos emeralds, while bumping into Sonic and his friends, who are trying to prevent their plan from becoming a reality. The Eclipse Cannon is activated and Eggman prepares to fire it while Sonic and Shadow are fighting each other, when suddenly a recorded message left by the professor activates.
Professor Gerald explains his slow journey into madness and insanity over Maria's death, and that the Ark will crash into earth in 30 minutes and destroy all life on it. To prevent the destruction of the earth, Sonic and his friends must go to the core of the cannon and stop the chaos emeralds from continuing the fast descent towards the earth. The cannon is guarded by the Biolizard, a previous test subject for Professor's discovery of Eternal Life.
Shadow, looking on in the observatory room alone, is greeted by Amy Rose, who begs him to help the others. Shadow's long lost memory of his promise to Maria returns to him. Realizing what he's done Shadow rushes to the cannon's cores to buy Sonic and Knuckles some time. Shadow defeats the Biolizard and Knuckles prays for the Master Emerald to stop the Chaos Emeralds from continuing the Ark's descent.
The Biolizard however teleports itself on the Ecplise Cannon to continue the Arks descent. Sonic and Shadow realize what they must do to save the world from destruction, so using the chaos emeralds Sonic and Shadow activate their Super Transformations and head towards the cannon. Sonic and Shadow defeat the Biolizard, but the Ark had already entered earths atmosphere and continues it's descent. Sonic and Shadow utilize their remaining power and perform Chaos Control to send the ark back into its original orbit at a safe distance from earth. Shadow being new to the super transformation blacked out and fell to earth, with everyone presuming he was dead, or so they thought.
Maria is Gerald Robotniks grandaughter and is Shadow the Hedgehog's best friend. Shadow and Maria were escaping from G.U.N soldiers, who were shutting down the Ark and all of Geralds experiments. Maria saved Shadow's life, pushing the launch pod button to send him to earth, sacrificing her own after a soldier shot her.
Rouge was Shadow's closest friend. When they first met Rouge had to protect the Master Emerald and steal jewels. Rouge was all into Shadow from 2001-every year on and out. In Sonic Rivals II, Rouge was Shadow's rival.
Sonic is Shadow's rival. They have known each other since the first game Shadow appeared in, Sonic Adventure 2. In Sonic Rivals II, Shadow was Sonic's mortal enemy.