Shadow the Hedgehog (シャドウ・ザ・ヘッジホッグ Shadō za Hejjihoggu?) is a fictional character from the Sonic the Hedgehog series. He is an anthropomorphic hedgehog/Black Arm hybrid and the arch-rival of Sonic the Hedgehog. Shadow was created as the "Ultimate Life Form" (究極生命体 Kyūkyoku Seimeitai?) by Gerald Robotnik, using the DNA of Black Doom, and is the end result of Project Shadow. His purpose was to provide ways to develop a cure for incurable deadly illnesses, more specifically for Gerald's granddaughter Maria Robotnik, but he was captured and put into stasis by the military when he was deemed as a threat to humanity.

Fifty years later, Shadow was released by Dr. Eggman in order to enlist him in his plan to conquer the world. Initially, Shadow worked with him, but secretly sought to destroy the planet in order to avenge Maria, who had been killed by the military, but was persuaded to help save it from Gerald's doomsday plans. In the process, Shadow lost his memories and as such, sought to uncover the truth of his past, during which he met Black Doom and the Black Arms; in the end, Shadow regained his memories, uncovered the truth and thwarted Black Doom's agenda and saved the world. From there, he continued his mission to protect humanity by becoming a special agent of GUN.

Shadow is sharp-witted, always on edge and has a strong sense of purpose, willing to accomplish his goals by any means.[2] Essentially a dark version of Sonic, Shadow can match him in both speed and skill, and can use Chaos Control with a Chaos Emerald. While preferring to work alone, he has helped Sonic and his allies when needed.