[3] It follows a main plot separate from all other Sonic the Hedgehog media, where Sonic has two siblings, Sonia and Manic, that are collectively part of a royal family who were forced to separate from their mother, Queen Aleena, upon Doctor Robotnik's takeover of Mobius due to a prophecy told by the Oracle of Delphius.

Along the way, they encounter other resistance groups against Robotnik and powerful artifacts that could wreak havoc on the world, all the while searching for their long-lost mother, Queen Aleena.

Meanwhile, Dr. Robotnik establishes an autocratic government by appointing bounty hunters Sleet and Dingo to do his dirty work, legally turning anyone who stands against him into robots devoid of free will, and forcing the nobles into paying large amounts of money to him as tribute.

Dr. Robotnik, with the assistance from Sleet, Dingo and the Swat-bots, tries constantly to capture the royal hedgehogs and prevent the prophecy from being fulfilled.

[11][12][13] 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.

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.

[27] In January 1999, it was announced that Bohbot Entertainment had acquired the North American broadcast rights to the series to air on their BKN syndicated strand.

[28] The series premiered in the country on 30 August 1999, on the company's then-new BKN Kids II on weekday mornings at 6:00 AM Central Time.,[29][30] and ran until 22 October 1999.

In 2009, reruns of Sonic Underground aired on Firestone Communications' Sorpresa, a Hispanic children's station (Channel 850 on Time Warner Cable) in the United States, broadcasting the audio-dubbed Latin Spanish dub.

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.

[41] In 2004, Anchor Bay UK obtained rights to distribute several DIC cartoons, including Sonic Underground on home video.

[49][50][51] David Cornelius of DVD Talk said, "While many Sonic fans did not take too well to all the changes, preferring the original 'Sonic' cartoon to this stranger, sometimes darker, sometimes sillier incarnation, the series did win a small but loyal cult following.

I fall more on the side of disappointment - for all the cleverness that went into crafting an all-new backstory, the episodes themselves are uninspired - but acknowledge the simple fact that it scores well with its target audience.

"[52] GamesRadar called the show as one of "the absolute worst Sonic moments", criticizing the extra characters and the complex plot.

Club panned the series, calling it one of the most artistic failures to ever end up on television and "the result of several unrelated ideas forcibly squashed into one project".

[53] Comedian Chris Hardwick commented on the show's theme song, composed by Mike Piccirillo, claiming that "that guy sounds like he's trying to win his exwife back.

In the story, Sonic Prime—hailing from the main universe in the comic series—joins forces with his counterpart and siblings to stop Dr. Robotnik, who has managed to assemble a monstrous battle machine known as the Giant Borg.