Sonic Underground was a French-American animated television series co-produced by DIC Productions, L.P., Les Studios Tex S.A.R.L. and TF1. It was the third Sonic The Hedgehog series made.
The show takes place in a separate canon and continuity than any other Sonic the Hedgehog media. Queen Aleena, the former ruler of Mobius, was overthrown by Dr. Robotnik and his lackeys Sleet and Dingo. Robotnik seized control of the planet and forced Queen Aleena into hiding. To preserve the dynasty, Queen Aleena separated her three children: Sonic, Manic, and Sonia after the Oracle of Delphius told her of a prophecy, proclaiming that one day, Queen Aleena would reunite with her children to form the "Council of Four," and overthrow Robotnik. Meanwhile, Dr. Robotnik did his best to set up an autocratic government, and legally turned anyone who stood against him into robots devoid of free will, and forced the nobles into paying large amounts of money to him as tribute.
When Sonic, Manic, and Sonia grew up, the Oracle of Delphius revealed the prophecy to them. After that, Sonic, Manic, and Sonia decided to go on a quest, searching throughout Mobius for Queen Aleena. Dr. Robotnik, with the assistance of the Swat-Bots and his bounty hunters Sleet and Dingo, tries constantly to capture the royal hedgehogs and prevent the prophecy from being fulfilled.
The Oracle of Delphius has assigned the three siblings powerful "medallions" that can change into musical instruments, and can also be used as weapons. Sonic's medallion is an electric guitar, Sonia's medallion is a keyboard that functions as a smoke machine, and Manic's medallion is a drum set that can be used as an "earth controller" with cymbals that can deflect laser-fire. All of the medallions can be used as laser guns. The three use the amulets not only to fight Robotnik's forces but also as instruments for their underground rock band, "Sonic Underground."
The show first aired in France from 6 January 1999 to 23 May 1999 on TF1, and then premiered in the United Kingdom on 2 May 1999 on ITV on the GMTV strand and finally in the United States in the syndicated children's block BKN Kids II on August 30th, 1999 and ended on October 22nd, 1999. It also aired on the Sci-Fi Channel on weekday mornings starting October 1999, lasting until October 2000. The show ran only for one season consisting of forty episodes. It was the first Sonic the Hedgehog television series to be sold on the iTunes Store.