|“||If I can't defeat Sonic then I hope Mobius is destroyed!||„|
|~ Doctor Robotnik threatening to destroy all of Mobius|
Doctor Robotnik is an evil dictator who was the main villain in Sonic Underground. He resembles the version of Robotnik that appeared in Sonic the Hedgehog (SatAM) and was voiced by Gary Chalk (who also voiced Grounder in Adventures of Sonic the Hedgehog).
Robotnik was assisted in his schemes by Sleet and Dingo. In the series finale Robotnik is defeated when 3 robots controlled by Sonic, Manic, and Sonia crashed into Robotropolis causing an explosion with Sonic stating "Game over, Robuttnik!".
Doctor Robotnik also has many different design changes. First off, he has a longer and more colored mustache then in the normal games. He also has an all metal arms after an incident that happened to him in the Underground. He also wears a long belt going around his waist. He wears shorter more colorful boots and a red cape. He also wears big, heavy yellow shoulder pads to hold up the cape. Dr. Robotnik was modified specifically to look like he was a mechanic.
Robotnik was a consistent villain throughout the series, but didn't appear in many of the episodes. One of the major things he did was in the beginning where he tried to destroy Sonic, but it then backfired when Sonic foiled his plans. He only captured Sonic successfully one time, and Manic multiple times. One of the more famous episodes was where Sonia was faced with a choice to save either Manic or Sonic. He is also notable for roboticizing Sonic's Uncle Chuck, Sonia's adoptive mother Lady Windimere, and Manic's adoptive father Ferral.
- Even though Dr. Robotnik is defeated in the final episode, his defeat was implied to not be permanent just like in much of the other episodes preceeding the series finale, and as Sonic and his brothers were never able to find their mother and fulfill the prophecy from the Oracle, it was never revealed if Sonic, Sonia and Manic restored peace on Mobius or if Doctor Robotnik defeated and robotized them, making this version of Robotnik not only a Karma Houdini (as he was never completely punished for his actions), but also one of the few versions of Dr. Eggman who was successful after all in taking over the world.
- Regarding the above, Archie Comics writer Ian Flynn initially intended to write an epilogue for Sonic Underground in the issue which ultimately became Sonic Universe #50, which would have likely concluded the series' narrative as well the fates of both Sonic, his brothers, their mother and Doctor Robotnik. However, as all Sonic Underground-material was off-limits, Flynn's epilogue proposal was dropped and replaced with a Metal Sonic story, as revealed by Flynn himself in 2012. With Sega ending its partnership with Archie in 2017 and starting a new Sonic the Hedgehog comic book series with IDW Publishing, such epilogue published by Archie is no longer a possibility.
- However, as of the events of the Sonic & Mega Man: Worlds Collide crossover storyline published by Archie in 2013, Sonic's current multiverse ceased to exist when Dr. Eggman launched the Super Genesis Wave in conjunction with Dr. Wily, causing the Prime Zone to be irreversibly rewritten and the multiverse to collapse in on itself, destroying most prior known realities. As the Sonic Underground reality is implied to have been one of them, it's likely that all its inhabitants were wiped away from existence, possibly implying that Doctor Robotnik was wiped away as well, which means that he at least got his karma yet also with the deaths of both his allies and enemies too, even Sonic and his brothers.