Main

• Sonic (speaking voice by Jaleel White and singing voice provided by Sam Vincent)^[4][5] is the eldest sibling and lead singer of many songs performed by the Sonic Underground. His medallion turns into a guitar, which can fire laser blasts. As fast as the speed of sound, Sonic can easily outrun danger. He is a big fan of chili dogs, causing him to be a bit overweight. He also has hydrophobia, being terrified of water as he cannot swim. Sonic wears anti-gravity sneakers that allow him to hover over the ground while running.
• Sonia (also a speaking voice by Jaleel White and singing voice provided by Stevie Vallance)^[5] is the only female hedgehog member of the Sonic Underground and the sister of Sonic and Manic. Unlike her brothers, she was raised by an aristocratic foster family, giving her an upper class mentality. She hates getting dirty, is skilled at gymnastics and karate, and possesses superhuman strength, a photographic memory, and the ability to spin in a cyclonic manner. Her medallion turns into a keyboard, which can fire laser blasts from one end, or create a pink mist when the keys are played. Sonia has a pink motorcycle which can travel as fast as Sonic's running and Manic's hover board (it was destroyed in the 36th episode). She also is the one that does research on Robotnik's plans and provides the technological innovation for the Sonic Underground. Of the siblings, Sonia is the only one to be seen involved in any romance, displaying feelings for her childhood friend Bartleby, despite his snobbishness, as well as other men encountered in her travels. Among these is Knuckles the Echidna, whom she develops an attraction to during the series' Flying Fortress saga.
• Manic (also a speaking voice by Jaleel White and singing voice provided by Tyley Ross^[5]) is the youngest sibling. He is a calculating and sarcastic hedgehog that was raised by thieves, and is a master of their trade. When Manic met his siblings, they disapproved of his thieving tendencies, but his skills as a lock-pick were greatly appreciated. Manic possesses neither Sonic's speed nor Sonia's spin-attack, thus making him the only member of the Sonic Underground who relies on entirely on his medallion for superpowers of his own. Despite his lack of superpowers, his thieving skills proves himself extremely useful to the group from time to time. Manic is the drummer of the Sonic Underground. His medallion turns into drums, which can cause earthquakes; the Oracle of Delphius claims that his drums are the most powerful instruments of the three. He also has a hover board that is as fast as Sonic's running and Sonia's motorcycle. His medallion's string is blue.
• Dr. Robotnik (voiced by Garry Chalk^[5]) is the evil human dictator of Mobius, renamed Robotropolis under his rule, having conquered it with his army of Swatbots. He captures and roboticizes anyone who opposes him, transforming them into robotic servants.
  • Sleet (voiced by Maurice LaMarche^[5]) is one of Robotnik's canine bounty hunters. This cunning wolf leads the bumbling Dingo about on missions to capture the hedgehogs. Sleet has a morphing device that can transform Dingo into anything he wishes. He is constantly being crushed by Dingo and is usually the one who suffers the most from their combined failures.
  • Dingo (voiced by Peter Wilds^[5]) is one of Robotnik's canine bounty hunters and Sleet's partner. Dingo is a huge, muscle-bound blonde dingo and is also very ignorant. He is partially roboticized in his hands and his left leg from the knee down, which is never explained. He has a relentless crush on Sonia, but remains fiercely loyal to Sleet.
  • Swatbots (voiced by Maurice LaMarche^[5]) are the robotic foot soldiers of Dr. Robotnik.

Recurring

• Queen Aleena Hedgehog (voiced by Gail Webster^[5]) is the mother of the Sonic Underground group and former ruler of Mobius before Robotnik's takeover. She had to give them up in order for the prophecy to become true. She spends the series on the run from her own children, until the time is right to reveal herself. Her character has many allies, including the Oracle of Delphius and Knuckles. She also does a bit of narrating in the start of every episode.
• Knuckles (voiced by Brian Drummond^[5]) is a red echidna who is the guardian of one of the Chaos Emeralds and Angel Island, and an acquaintance of Queen Aleena's. He is very protective of his island home, and has set many traps about the island. He has a pet dinosaur called Chomps, and like his game incarnation is shown to be somewhat gullible. His great-grandfather Athair warns him that he must stay on the island in order to play his part in the freedom of Mobius. He turned against the Hedgehogs twice - first being tricked into thinking they were thieves and later thinking that it was the only way to save their planet - but came around and worked with them against the threat of Robotnik and his henchmen. During the Flying Fortress arc, he showed signs of a growing affection for Sonia, including a particular guilt over the prospect of betraying her.
• Oracle of Delphius (voiced by Maurice LaMarche^[5]) is an odd, wart-covered in a cloak that resembles a scaly anteater. The Oracle prophesied that when Robotnik invaded Mobius, Aleena and her children would form the Council of Four to overthrow Robotnik and free Mobius. The Oracle lives in a cave somewhere in a cold region of Mobius, and is quite good at making chili dogs. He is named after the Oracle at Delphi.
• Sir Bartleby Montclair is a posh, cowardly mink who is one of Robotropolis' richest aristocrats. Bartleby was Sonia's fiancé. He dislikes Dr. Robotnik and is often forced to fund Robotnik's schemes – although in secret he still supports Aleena. He speaks with an upper-class English accent.
• Cyrus (voiced by Ian James Corlett^[5]) is a lion and a technician for the Freedom Fighters. He is an old friend of Sonic. In his first appearance he was working as a spy for Robotnik, but quit upon discovering that the Freedom Fighters' Sanctuary was a hideout for their children. Cyrus's father was roboticized.
• Trevor is a mouse who is a friend of the royal siblings and Cyrus. He dresses like a hippie. Trevor is an ace pilot and helps build and fix mechanical equipment.

Development

It is often claimed that the newly Sega of America CEO Shoichiro Irimajiri contacted DIC CEO Andy Heyward to make a new Sonic cartoon, which would help gain interest in buying their new console, the Dreamcast.^{[citation needed]} Sonic Underground started production in early 1997, around the same time the development of both the Dreamcast and Sonic Adventure had started. The show bible was written as early as March 1997.^[8][9] The show was publicly announced as early as December 1997.^[10][11][12]

When the show was in development, two episodes per week were produced, and the writers felt that they were not given enough time to "tie everything together" in the plot, being limited to a three-part "Origins" saga for coherency. DIC used cattle calls to generate episode plots. Periodically, about twenty unaffiliated writers were brought into the studios to learn about the established characters and brainstorm possible plots for episodes, after which about one or two would be selected.^[13] According to Mike Piccirillo, when he was writing songs for the show, there were no storyboards done yet, so he could only work off of the scripts, which often said what moral or lesson the song should be about in each episode.^[14][15] The show's animation was outsourced to the Taiwanese animation studio Hong Ying Animation with the storyboards and main title animation done in Madrid, Spain by Milimetros, S.A. (also responsible for the animation in the Saturday morning Sonic the Hedgehog cartoon and some of the storyboards in Adventures of Sonic the Hedgehog), pre-production services provided by Le Studio Ellipse, layout services by Arles Animation and video and audio post-production services by Les Studios de Saint-Ouen. According to Robby London, Sega of Japan had an active role in the approval process for Sonic Underground, going so far as to force DiC to reanimate the characters with five fingers instead of the usual four due to the Japanese association of four fingers with the yakuza.^[16][17]

While it was once believed that 65 episodes were made of which only 40 aired, Ben Hurst, a main writer from Sonic the Hedgehog (dubbed SatAM by fans), who was also involved in Sonic Underground's production, stated in a chat at the Sonic Amateur Games Expo 2008^[18] that only 40 were planned to be produced from the beginning.^[19]

Airing and Broadcast

United States

In the United States, Sterling Entertainment released a VHS/DVD titled "Dr. Robotnik's Revenge" in July 2003, containing three episodes, and a bonus Super Mario Bros. episode on the DVD release. It was re-released by NCircle Entertainment in March 2007 without the bonus Mario episode. The Sterling versions of the Adventures of Super Mario Bros. 3 "King Koopa Katastrophe" and The Legend of Zelda "Ganon's Evil Tower" DVDs also included 1 and 2 episodes respectively as DVD bonuses which the NCircle reissues of both releases excluded. Sterling Entertainment's VHS/DVD release of Sonic Christmas Blast also included 3 episodes (2 on the VHS).

Shout! Factory and Vivendi Entertainment have released the complete series on DVD in Region 1 (NTSC) in two volume sets. Volume 1, simply entitled Sonic Underground, was released on December 18, 2007.^[37] It contains the first 20 episodes of the show on three discs, with disc three also including interviews with DIC's Robby London, Mike Piccirillo, an opening title animatic, and concept art. A bonus fourth disc is an audio CD containing eight songs from the series, including the opening theme. Sonic Underground: Volume 2 was released on 17 June 2008, featuring the remaining 20 episodes and another bonus audio CD featuring eight more songs from the series.

From 2007 until 2010, NCircle Entertainment released several single-release DVDs containing four episodes each:

NCircle also re-released Volumes 1 and 2 in 2013 and 2017, respectively.^[38][39] On July 25, 2023, they released the complete series as a four disc set.^[40]

United Kingdom

In 2004, Anchor Bay UK obtained rights to distribute several DIC cartoons, including Sonic Underground on home video. The first two volumes were released on May 31, 2004^[41][42] while the next two were released on August 16, 2004.^[43][44] There were plans for the remaining six volumes to be released separately, but they were instead released in a 10-DVD boxset in October 2004.^[45][46]

In July 2005, Avenue Entertainment released two budget DVDs containing two episodes each.

Delta Home Entertainment released the complete series again on DVD in June 2008 as a 4-disc set, with the fifth DVD containing the bonus features from the Shout! Factory DVD boxset.^[47] Delta Home Entertainment also released the four discs separately, with Disc 1 and 2 being released as "Beginnings" and "Who Do You Think You Are" in August 2008, and Discs 3 and 4 being released as "When in Rome" and "Country Crisis" in September 2008.