Sonic the Hedgehog is a media franchise owned by Sega, centering on a series of high-speed platform games. Sonic, the protagonist, is an anthropomorphic blue hedgehog with supersonic speed. Typically, Sonic must stop antagonist Doctor Eggman's plans for world domination, often helped by his friends, such as Tails, Amy, and Knuckles.

The first Sonic the Hedgehog game, released in 1991, was conceived by Sega's Sonic Team division after Sega requested a new mascot character to replace Alex Kidd and compete with Nintendo's mascot Mario. Its success spawned many sequels and helped Sega become one of the leading video game companies during the 16-bit era of the early 1990s. The first major 3D Sonic game, Sonic Adventure, was released in 1998 for the Dreamcast. Spin-offs have explored other genres, including racing games such as Sonic R (1997) and sports games such as Mario & Sonic at the Olympic Games (2007).

By March 2011, the series had sold over 89 million physical copies,[n 1] and grossed over $5 billion by 2014. As of 2018, the series has shifted 800 million copies, including free-to-play mobile game downloads. Several Sonic games are often included in lists of the greatest games of all time. Along with video games, the Sonic franchise has also crossed over into a variety of different media, including animation, comic books, and a Hollywood film.