Unmarked spoilers below.
- Dr. Ivo Robotnik, better known as Dr. Eggman, frequently showcases himself as one of Sonic's most magnificent foes throughout his various appearances Depending on the Writer:
- SegaSonic the Hedgehog: Dr. Eggman's objective in this game is to kill Sonic, Mighty and Ray. He starts out by successfully kidnapping them before imprisoning them in Eggman Island, an entire island designed to kill them. Then, he attempts to kill them in their prison with an advancing wall of spikes. When they escape, Eggman tries to kill them in the most over-the-top ways through the levels, with a giant ball of lava, falling giant stalactites, collapsing sand areas, giant rolling cylinders, boulders, trapped ladders, water and spike mines. He also traps the bridge leading towards his tower, expecting the heroes to cross it, and said trap ends up working. When the heroic trio confronts him, he successfully escapes and activate the tower's self-destruct sequence with only 20 seconds to spare. Leaving Sonic, Mighty and Ray screaming and panicking through the whole game, Eggman, despite being hammy, reminded them that his I.Q. of 300 wasn't for show.
- Sonic Adventure: Dr. Eggman's objective in this game is to destroy Station Square in order to build his own city, Robotnikland. To do so, he freed Chaos and turned him into his ally. Since Chaos grows stronger by absorbing the Chaos Emeralds (and would eventually destroy Station Square once he has all seven), he decides to collect them. As such, he attacks Sonic and Tails to steal their Chaos Emerald. Despite his defeat, he succeeds in stealing the Emerald when they are distracted. He then revealed to them his plan, expecting them to collect the Emeralds before him, which would allow him to easily steal them. While his plan works, he also collect two emeralds by himself, obtaining 6 Emeralds. When Chaos 6 is defeated by Sonic and Knuckles, Eggman fires a missile at Station Square, only falling because of the missile malfunctioning and Tails' interference. Despite his silly, over-the-top attitude, Eggman remained constantly a step ahead of the heroes for half of the story, reminding you why he's Sonic's archnemesis.
- Sonic Lost World: This version of Dr. Eggman starts off with complete control of the Deadly Six through the use of the Cacophonic Conch and only loses them due to Sonic's recklessness. Now stripped of his machines and resources, Eggman decides to ally with Sonic and Tails and take advantage of his past habit of uniting against a stronger force. He even goes so far to save a suspicious Tails's life to make his alliance seem completely altruistic. In the climax, Eggman seemingly sacrifices his life so Sonic can defeat the Deadly Six, but Eggman faked it by using a jetpack to break his fall. Spending the time beneath notice building a mech powered by the energy the Extractor had absorbed, Eggman claws his way back to Final Boss status in a stunning display of manipulation and patience.
- Sonic Forces: In this work Dr. Eggman researches the Phantom Ruby in his attempt at world domination. Recruiting Infinite through promises, he implants him with a Phantom Ruby prototype and christens him as the Eggman Empire's high commander. With everything in place, Eggman lures Sonic into a savage beatdown, and with him out of the way, conquers the world in a matter of months. Eggman proceeds to display foresight and cunning in trying to keep his iron-fisted hold on the planet—ordering his forces to destroy any remaining prototypes, keeping multiple power sources unbeknownst to his enemies, and targeting critical points in the Resistance. He also factored in multiple ways to eliminate the Resistance outright, culminating in a virtual Colony Drop when they were gathered in one place. Even in the final fight, Eggman pulled out all the stops, having kept the real Phantom Ruby with the whole time and had to be stopped by the combined might of Sonic, Classic Sonic, and the Avatar.
Other Video Game characters
- Sonic Adventure 2: Shadow the Hedgehog was an Ultimate Lifeform that lost his best friend Maria and his creator Dr. Gerald Robotnik when they were killed by the government. Imprisoned but eventually released by Geralds grandson, Dr. Eggman Robotnik, Shadow enacted a plan to destroy all of humanity as revenge. Playing on Eggmans ego and his grandfathers legacy, Shadow manipulated the doctor into gathering Chaos Emeralds, misdirecting everyone into thinking it was for powering a Kill Sat. This diverted everyones attention from his real plan of performing a Colony Drop. He even manages to expose Rouge as a government agent. Shadows plan is only foiled because Amy Rose helps him remember Marias final request for Shadow to protect the people of Earth and so he decides to help stop his own scheme, almost sacrificing himself. Shadow, in his first appearance, was as devious as Sonic villains come and even as a hero is one of the franchises most competent characters.
- Sonic Heroes: Metal Sonic gains enough sentience to overthrow Dr. Eggman and graduate into a much more serious threat. Flawlessly impersonating his creator, Metal Sonic issues a challenge to Team Sonic that would either end in him obtaining their data in their counterattack or conquering the world to start a "robot kingdom." Disguising himself as the real Sonic, Metal Sonic kidnaps Chocola Chao and Froggy to gain the data of Chaos and its shapeshifting abilities. He also lures Team Sonic with the Egg Albatross in Bullet Station to buy time for the Egg Fleet to deploy. Despite the involvement of four different capable teams, Metal Sonic takes everything in stride under the radar, acquiring more data than initially planned and playing them all until Dr. Eggman's real location is discovered. Although his statements as Metal Overlord bring his sanity to question, Metal Sonic remains one of Sonic's most dangerous foes. Even after being reprogrammed to be obedient, Metal Sonic showed his penchant for undercover gambiteering when he copied the data of all World Grand Prix participants for one final Extreme Gear race.
- Sonic Storybook Series: From Sonic and the Black Knight, Merlina the Wizard flawlessly masterminded the entire plot of the game completely beneath notice. Summoning Sonic from his world to slay a corrupted King Arthur, she takes the arcane Scabbard of Excalibur to utilize its power of immortality, casting a powerful spell on the Kingdom of Camelot. Having foreseen the ruinous future of her world, a despairing Merlina places Camelot under a kind of magical stasis, fueled by the dark forces from the Underworld, in hopes of keeping it eternal. Showing absolute conviction to her cause, Merlina even fights back against Sonic and Caliburn as the Dark Queen. Although ultimately defeated, Sonic spares and convinces Merlina to abandon her nihilistic outlook, proving her to be a lost, if understandable soul who needed her hope restored after resorting to extreme measures to keep her world intact.
- Sonic the Hedgehog (Archie Comics): Mammoth Mogul is a cultured, ancient wizard with a persistent desire to Take Over the World. It is he who founded the Order of Ixis as one of many attempts in gathering an army to serve him in his conquests. A mammoth with powerful rhetoric, Mogul is not above convincing people to his side through words alone while simultaneously planning on how to use them for his own ends. This is best displayed when Mogul led Mighty, Tails, and Mina to suicidal situations to make Sonic submit and become part of his new Fearsome Foursome. Even so, Mogul is all too willing to make the universe bow to his will, shown when he becomes the all-powerful Master Mogul and tried to take over alternate universes. After one too many defeats despite his variety of schemes, Mammoth Mogul contents himself with living the life of a businessman, patiently waiting until Sonic and his allies grow too old to oppose an immortal wizard like himself.
- Sonic the Hedgehog (IDW): Metal Sonic, having underwent upgrades during the events of Sonic Forces, discovers that the Eggman Empire has been defeated and that Eggman himself has gone missing. Shapeshifting into Eggman and ruling the empire in his place, Metal Sonic leads coordinated attacks across the world while searching for Eggman to have him regain his place as ruler of the Empire. After discovering that Knuckles is on the surface from his observations of Sonic, Metal Sonic takes over the unprotected Angel Island and obtains the Master Emerald, ensuring that he'll be able to negate Sonic's Super form if he tries to use it. Even when defeated, the mercy of the heroes allows Metal Sonic to find the amnesiac Eggman and succesfully restore his memories leading Eggman to return to his old ways. After the events of the Metal Virus, Metal Sonic single-handedy buys time for Eggman to escape by lying in wait and critically injuring Gemerl when the latter is about to apprehend Eggman. Proving to be as cunning as he was during Sonic Heroes while maintaining his loyalty to the doctor, Metal Sonic shows why Eggman views him as his greatest creation.
- Dark Oak, supreme leader of the Metarex, is a chilling combination of power and tragedy. Originally an alien lifeform named Lukas, he fell out with his lover Earthia and parts of his own species trying to save his world from destruction. His ambition and sound intentions eventually corrupted him to become Dark Oak, an Evil Overlord bent on creating a galaxy free of war and conflict by annihilating everything except plants and botanical lifeforms like himself. Introduced trouncing Super Sonic in an attempt to get all seven Chaos Emeralds, Dark Oak strays to the background and creates strategies to systematically crush his opposition that, even in failure, will give him an idea of what they are capable of. Dark Oak's cruelest but most ingenious act was forcing a sleeper agent within the ranks of Sonic and crew from the very beginning. Said person had a tracking device that relayed valuable information to the Metarex as they captured the Chaos Emeralds and the Planet Eggs for "Forestation." At the end of a hard-fought battle, Lukas dies realizing the errors of his ways and reconciles with Earthia in the afterlife.
- Shadow the Hedgehog, the Ultimate life form, lost his best friend Maria and his creator Dr. Gerald Robotnik when they were killed by G.U.N. in the Space Colony ARK. Desiring revenge, when Gerald's grandson Dr. Eggman released him, he manipulated him into gathering all seven Chaos Emeralds and putting them in the ARK's Eclipse Cannon, which in truth would lead to a Colony Drop. Shadow's plan was only foiled when Chris convinces him to help save the world. He would have died doing so if Eggman didn't save his comatose body. Amnesiac, he returns and saves Chris from death, destroys a Metarex and retrieves an Emerald for Eggman out of gratefulness. Learning that Cosmo is a sleeper agent for the Metarex, he tries to kill her. In his attempt, he outsmarts Tails thrice by hacking into the Blue Typhoon's heat source search program, then into the ship's camera system when Tails locks the heat program and by teleporting back in the ship when Tails launched him into space. Only stopped in his attempt by Cosmo's amulet teleporting him, Shadow helps the heroes in the final battle against the Metarex. After attempting to save Cosmo from Final Mova, he sacrifices himself by moving everyone to safety as Final Mova exploded. Ruthless but caring, Shadow surpassed his game counterpart in sheer audacity and brilliance.
- Rouge the Bat is a thief obsessed with jewels, starting a stealing spree upon appearing on Earth. Once she learns the location of a Chaos Emerald, she misdirects Sonic while she collects the emerald. However, it was a trap from G.U.N. : she improvises by accepting to become a G.U.N. agent and in return, is granted immunity and keeps her loot. When E-70 Noizi almost defeated her by using her weakness to sound, she used a bomb attached to her wrist to win. Unlike her game counterpart, she succeeds in stealing the Master Emerald during the "Shadow Saga" and joined Eggman and Shadow while hiding her loyalty to G.U.N.. When she later participates in a tournament for a Chaos Emerald, she fights Tails who's stronger than expected. She wins by kissing him and then throwing him out of the ring. When facing Knuckles, she has him agree to fight inside a dark tent, making him fight blind. During the Metarex Saga, she blackmails Bokkun into suggesting to Eggman a plan to obtain an emerald for himself, while she plans to swoop in and steal it. Skilled and manipulative, Rouge was one of the anime's most competent characters.