Shadow the Hedgehog is a character created by the Japanese game developers Takashi Iizuka, Shiro Maekawa, and Kazuyuki Hoshino. He is a major character in Sega's Sonic the Hedgehog franchise. An anthropomorphic black hedgehog, Shadow shares design traits and attributes with Sonic the Hedgehog, and serves as Sonic's principal rival throughout the franchise. Described as an antihero, Shadow is portrayed as having noble intentions and a compassionate heart, but is standoff-ish with the people he encounters and often willing to fight anyone who comes in the way of his objective. His solemn demeanor and antagonistic traits put him at ideological odds with Sonic, though the two have a begrudging respect for each other and frequently team up for the greater good. Kōji Yusa voices Shadow in Japan, while his English voice has been provided by David Humphrey, Jason Griffith, and Kirk Thornton. Keanu Reeves voices him in the feature film Sonic the Hedgehog 3 (2024).

Shadow first appeared in the Dreamcast game Sonic Adventure 2 (2001), although he was conceived during the development of Sonic Adventure (1998). Iizuka devised the concept, while Maekawa developed his character and Hoshino designed him. Influences included the Dragon Ball character Vegeta, the Image Comics character Spawn, the Sonic character Metal Sonic, kabuki makeup and speed skaters. Sonic Team envisioned Shadow as a one-off character who would only appear in Sonic Adventure 2, but his popularity among fans led to his inclusion in subsequent games, beginning with Sonic Heroes (2003), in which he becomes part of "Team Dark" alongside Rouge the Bat and E-123 Omega. Shadow has since featured in many Sonic games, including serving as the main protagonist of the games Shadow the Hedgehog (2005) and Shadow Generations (2024).

Shadow is one of the few Sonic characters to have a character arc across multiple games. Shadow was created by Professor Gerald Robotnik, the grandfather of series main antagonist Doctor Eggman, using alien DNA with the intention of creating the "Ultimate Lifeform". He was housed on a space colony, the ARK, where he developed a close friendship with Robotnik's granddaughter, Maria Robotnik. However, the government organization G.U.N., upon discovering Robotnik's schemes on conquering the world, invaded the ARK and killed its occupants, including Maria, before capturing Shadow and keeping him in stasis for fifty years. After escaping, he initially plots revenge and desires to annihilate humanity for Maria's death, but later remembers his promise to her that he would protect the world from danger and allies with Sonic against Robotnik's own revenge plans. Shadow is presumed dead in the battle, but is in actuality kept comatose and with amnesia by Eggman. After being freed by Rouge, he begins recovering his memories and goes on a quest to continue protecting the world, reaffirming his promise and gaining a stronger sense of identity upon doing so.

Shadow is one of the most popular Sonic characters and was named one of the greatest video game characters by Guinness World Records in 2011. However, he has proven divisive among video game journalists. Some praised his role in Sonic Adventure 2 and his levels' preservation of the Sonic theme, but others criticized his dark and brooding characterization, particularly in later games, and ranked him among the worst Sonic characters. The Shadow the Hedgehog game received generally unfavorable reviews, though it sold well. In the third installment of the Sonic the Hedgehog film franchise, Reeves's adaptation received critical praise for his moody portrayal of the character's stoicism, empathy and darkness.

Shadow is an anthropomorphic black hedgehog appearing in Sega's Sonic the Hedgehog series of platform games and its various spin-offs. He first appeared in the 2001 installment Sonic Adventure 2, the final Sonic game released for a Sega video game console. His roles in the games vary. Some, such as the main series games Sonic Adventure 2, Sonic Heroes (2003), and Sonic the Hedgehog (2006) feature him as a major playable character, and he is the protagonist of the spin-off Shadow the Hedgehog (2005) and a downloadable content (DLC) package for Sonic Forces (2017). Shadow also appears as an unlockable playable character in Sonic Dream Team, after an update in 2024 to commemorate the Year of Shadow campaign. Others, such as the anniversary game Sonic Generations (2011), limit him to a non-playable role. He also appears as one of the characters who can be summoned using the Assist Trophy item in the Super Smash Bros. series.

Shadow is a mysterious, sharp-witted, and brooding antihero. While his ultimate goal is to protect the world from danger, he dislikes humanity, and once he has set a goal, he does whatever it takes to accomplish it. This often causes him to take risks without thinking them through and puts him at odds with series protagonist Sonic the Hedgehog. Although a loner, Shadow collaborates with treasure hunter Rouge the Bat and robot E-123 Omega in games such as Sonic Heroes, Sonic the Hedgehog (2006), and Sonic Forces. Shadow allies with Sonic in some games, but also does so with Doctor Eggman in Sonic Adventure 2 and Shadow the Hedgehog.

Shadow shares many similarities with Sonic. Visually, GameSpot's Ben Stahl described Shadow as "an evil version of Sonic himself—similar in appearance, but with darker skin, more angled eyes, and a fearsome snarl instead of Sonic's trademark grin." GamesRadar+'s Justin Leeper said that if Sonic was Superman, then Shadow would be his Batman. The characters control similarly in games, as both share skills and the ability to run at great speeds. Shadow has unique attributes in some games, such as his uses of firearms and vehicles in Shadow the Hedgehog and Sonic the Hedgehog, respectively. He can also use the Chaos Emeralds to perform "Chaos Control"—allowing him to distort time—and create weapons like spears. Like Sonic, Shadow can transform into a "Super" form, giving him special powers.

Outside of the video game series, Shadow appears in the anime series Sonic X (2003-2006), which adapts the story of the Sonic Adventure games, as well as Sonic Boom and Sonic Prime. The original Japanese cast from the games reprised their roles for the former, while Jason Griffith (who also voiced Sonic) voiced Shadow in its English dub by 4Kids Entertainment. In the Sonic Boom (2014–2017) spin-off franchise, Shadow appears in the 2014 games Sonic Boom: Rise of Lyric for the Wii U and Sonic Boom: Shattered Crystal for the Nintendo 3DS, as well as the television episodes "It Takes a Village to Defeat a Hedgehog" and "Eggman: The Video Game", voiced by Kirk Thornton (who also voiced Orbot).