In the Sonic the Hedgehog fictional universe, the Biolizard (code-named Project Shadow) was created by Professor Gerald Robotnik about thirty years ago.

It was designed to be the ultimate life form. When GUN came to Ark they found the Biolizard and shut it down. It didn't go without a fight however and it destroyed almost the entire group of GUN officers.

While the Biolizard was being created, Robotnik and his grandaughter Maria created Shadow the Hedgehog. They programmed him with artificial memories about being created and knowing Maria. Shadow's last memory was that GUN attacked the space colony ARK and shot Maria, killing her in the process. He sent him to Earth (Mobius in the comics and some games) to make the people there happy. The flaw though to this is that it was a theory created by fans (the artificial memories) and due to the upcoming game "Shadow the Hedgehog" as well as other sources (Gerald Robotnik's Diary as one) also prove this false.

Meanwhile, the Biolizard remained in suspended animation until Sonic the Hedgehog and his crew came to ARK. After Sonic stopped Eggman from destroying Earth a video of Prof. Gerald came online warning people of Shadow. Sonic and Eggman joined forces and helped to deactivate the Eclipse Cannon.

The Biolizard was awoken and pulled ARK into Earth's atmosphere causing it to fall. Amy Rose convinced Shadow to help save the Earth. He remembered Maria's wish and helped Sonic and Knuckles get to the Chaos Emeralds. Shadow fought the Biolizard only for it to use Chaos Control and fuse with ARK, becoming The Finalhazard. Using the Chaos Emeralds Sonic and Shadow became Super Sonic and Super Shadow and fought The Finalhazard. Using Finalhazard's wounds to hurt him Sonic and Shadow killed the Finalhazard and stopped ARK from crashing into Earth. Shadow lost his life in the process.