Doctor Eggman (a.k.a Doctor Robotnik) is a character who constantly appears in the Sonic For Hire series.
Dr. Eggman makes his first appearance in the series episode "Robotnik" when at the time Sonic was looking for work and Dr. Eggman happened to have a job for him which involved cleaning out his toilet, soon after he explained that the entire place was like a toilet and explaining he was a Podiatrist doctor, Sonic finished the work and Dr. Eggman acted as though he was going to pay Sonic when he promptly yelled out "Fuck you, stink ball!" and then ran off.
He then made his next appearance in the series episode "Street Fighter" where he made it his business to annoy Sonic and Tails when they were working as announcers for the Street Fighter battles and completely ignored the fact he didn't pay Sonic for the work he done and then pulled a prank on Tails by marking the Tornado with graffiti labeled "Pecker Face" then after managed to put the blame and shock on Sonic for throwing a glass bottle at Blanka.
He then made a short visit in the series episode "Burger Time" after mocking Sonic for the way he cleaned out his toilet, he went on to order 4 burgers and devoured them before briefly choking, still oblivious to the fact Sonic creamed on his burgers.
Dr. Eggman next appeared on the series episode "Tetris" when he came back for his revenge on Sonic, assuming he made the special sauce on his burgers extra salty so it would raise his blood pressure, still oblivious to what really happened and went on to state he always spits the special sauce out, so Sonic never really won in the end, then after released Earthworm Jim from the back of his Egg Mobile only for it to break down on him, which lead him to accompanying Sonic and Earthworm Jim to Mother Brain's home to retrieve Earthworm Jim's suite.
He didn't appear again until "Double Dragon," where Eggman is called by Sonic (along with Earthworm Jim again) to assist him in his job to take down the brothers. Although he and Earthworm Jim were taken down very easily by the brothers, taking away Eggman's credibility as an antagonist and making him a joke character. In "The Battle Part 02," Eggman along with Kirby, Earthworm Jim, and Gilius Thunderhead come to assist Sonic in his battle with Mario and a bunch of various villians. He claims that if Sonic dies then his life won't have any meaning, but Sonic laughs at how sappy he's acting. According to Eggman, his minions left him because his new name didn't demand much respect.
He becomes a tritagonist in Season 3 until the end where he and Earthworm Jim stay in South America to snort piles of cocaine and have fun with girls. His role in season three until that episode consited of helping Sonic out in episodes such as "Link" "Peach" "Casino Zone 1-3" "The War 1-2" and "Tecmo Bowl". It seems that despite the fact they still dislike eachother, Sonic and Eggman have become allies. Eggman helped Sonic rob Casino zone in the casino zone saga, and formulated the whole plan to rob casino zone...which failed until Tails came up with a plan to rob the vault with Sonic's help.
In Season 4, him and Earthworm Jim were mentioned by Kirby in "Sonic For Hire: Two Bad Characters" so they can bring them back so they can be in the movie. They are brought back in "El Padrino" but they only left because Hollywood invented coke on tits. In Sonic For Hire: Movie Magic, He's in the film, Two Bad Characters, but still is waiting for his coke and tits. In "Two Bad Characters" Eggman is enjoying the movie and pleased that he nailed his parts, but is excitement is faded sortly when sonic interupts the movie to kill Tails.
In season 5, Eggman survived the blast (Along with Earthworm Jim) and appearsin "Joust" He has forgiven sonic for his crazy assasin plan, and explains him and Jim (and probably a bunch of other characters) got the hell out of the theather knowing something was up when they saw sonic's face on the movie screen. In Sonic For Hire: Asteroids, Eggman and Jim met Frank and got some Buffalo Wild Wings. In "Sonic For Hire: Destory Venom" he, along with the rest of the crew, go out on a mission to battle with planet Venom. He accidently drops his wallet into a deep fryer (the deep fryer was in his ship) and proceeds to eat it after getting it out of the hot oil. In "Rocket Knight Adventures" he is relaxing in a hot tub with Sonic and Tails until he revealed to everybody about an erection that he had, which he claims that it'll be around for 4 to 6 hours. He then ditches the Earthworm Jim, Sonic, Tails, and a solder to go party with some of the zergs, who jump him and steal some of his DNA in "Starcraft".
Eggman appears in "Chrono Trigger" where he is dressed up as Sonic and has sex with Lucca. (which results in him being the father of Lucca's twin children instead of Sonic) He reappears in "Sonic Knuckles" where Sonic travels back in time to the 90s and meets Knuckles's past self and they both defeat past Eggman. Future Eggman then proceeds to steal the Epoch from Sonic so he could rule the world, only for him to end up becoming morbidly obese due to inventing the Taco Sandwitch, (two tacos for bread and ten tacos in the middle) It caused him to have his badniks wash his fat flaps and wipe his ass. When Sonic fixes Time, Eggman is normal, and later when Sonic gets kidnapped by the Avengers, Eggman...doesn't do anything, but later goes to prank Mario with Tails and Jim only to find Sonic's dead. They later revive him using three time machines, but that cause Mario to be a chicken Farmer, Tails to be freakishly huge, Jim to be a Yoshi, Sonic to later become Wario, time to get messed up, and Eggman ends up as a baby.
In "Back to Work", he appeared in the pants for the only time in the series. Later in "Elevator Action", he wrote a Bucket List.