
The Sonic the Hedgehog video game franchise began in 1991 with the game Sonic the Hedgehog for the Sega Genesis, which pitted a blue anthropomorphic hedgehog named Sonic against a rotund male human villain named Doctor Eggman. The sequel, Sonic 2, gave Sonic a fox friend named Tails. Sonic CD introduced Amy Rose, a female hedgehog with a persistent crush on Sonic. Sonic 3 introduced Knuckles the Echidna, Sonic's rival and, later, friend. All five of these have remained major characters and appeared in dozens of games.

Chao are fictional life-forms in the Sonic the Hedgehog video game series published by Sega. They are small, childlike creatures that go through a complex life cycle and exist in several visual forms depending on how they are raised. Developer Sonic Team incorporated Chao into the games to encourage players to explore levels and support the good–evil dichotomy of Sonic Adventure 2.

Sonic the Hedgehog is an animated television series based on the video game series of the same name. It was story edited by Len Janson and produced by DIC Productions, L.P., Sega of America, Inc., and the Italian studio Reteitalia S.p.A. in association with Telecinco. It is the second of DiC's Sonic cartoons, following Adventures of Sonic the Hedgehog. It features a more dramatic and dark story than the lighter Adventures series, depicting Sonic as a member of a band of freedom fighters battling to overthrow Doctor Robotnik, now a despotic dictator who conquered their home planet Mobius years prior, ruling it as a polluted industrial dystopia. To distinguish it from other Sonic the Hedgehog media, the series is commonly referred to by fans as "SatAM", in reference to its Saturday morning timeslot.

Doctor Ivo "Eggman" Robotnik is a middle-aged Overlander and the main antagonist of Sega's Sonic the Hedgehog series. Eggman was created and designed by Naoto Ohshima as part of many design choices for Sega's new mascot. After the creation of Sonic the Hedgehog, Ohshima chose to use his previous egg-shaped character to create the antagonist of the 1991 video game Sonic the Hedgehog, making him the arch-nemesis of the series' eponymous main character.

Sonic Battle is a 2003 fighting video game developed by Sonic Team for the Game Boy Advance. It is the second fighting game in the Sonic the Hedgehog series, the first game being Sonic the Fighters. It is the sequel to 2002's Sonic Advance 2 and was released in Japan in December 2003 and in North America and Europe in early 2004.

Knuckles the Echidna is a fictional character and one of the main characters in Sega's Sonic the Hedgehog series. He is a red anthropomorphic short-beaked echidna who is determined and serious, but sometimes gullible. He has the ability to glide and climb up walls, and is a powerful fighter with spiked hands. He serves as the guardian of the Master Emerald, a huge gemstone that controls the series' integral Chaos Emeralds, and is the last living member of his tribe, the Knuckles Clan.

Shadow the Hedgehog is a fictional character appearing in Sega's Sonic the Hedgehog video game franchise. Shadow was created by Takashi Iizuka and Shiro Maekawa, and debuted in the series' 2001 installment Sonic Adventure 2. Although this was intended to be his only appearance, Shadow proved so popular among fans that developer Sonic Team decided to include him in 2003's Sonic Heroes. Shadow has since featured in numerous entries in the franchise, including a game of his own in 2005 Shadow the Hedgehog. He also appears in Sonic television adaptations, comics, and merchandise.

Sonic the Hedgehog is the title character and the protagonist of the Sonic the Hedgehog video game series published by Sega, as well as numerous spin-off comics, animations, and other media. Sonic is a blue anthropomorphic hedgehog who can run at supersonic speeds and curl into a ball, primarily to attack enemies. In most games, Sonic must race through levels, collecting power-up rings and avoiding obstacles and enemies.

Miles Prower , better known by his nickname Tails , is a fictional character in Sega's Sonic the Hedgehog series, and the title character's best friend, sidekick, and most recurring ally. Tails also appears in his own spin-off series, comic books, cartoons, and films. He is the second character to consistently appear by Sonic's side in the series. The name "Miles Prower" is a pun on "miles per hour", a reference to the famed speed of Sonic the Hedgehog. He is a two-tailed fox, hence the nickname. A mechanical genius and skilled pilot, he can fly by spinning his tails like a helicopter rotor and can be seen flying in multiple games and TV shows created by SEGA. He debuted in November 1992 with the release of Sonic the Hedgehog 2. In the mid-1990s, he was featured as the main character in a number of spinoff games: Tails and the Music Maker for the Sega Pico, and Tails Adventure and Tails' Skypatrol for the Game Gear. Tails was rated the third-most-popular character in the franchise, behind Sonic and Shadow, in an official poll from Sega in 2009.