Franchise: Sonic The Hedgehog

Dr. Robotnik was created to be the opposite of Sonic, and to be the bad guy. During the development of the game, there was a growing debate between developers and environmentalists, and Robotnik was created to represent machinery and development, as apposed to Sonic, who represented the environment.

His egg shaped redesign came from Naoto Ōshima wanting to give the characters designs that were easy enough for kids to draw.

The English script for Sonic Colors, as well as other 3D Sonic localizations up to Sonic Forces, was partially written by Ken Pontac, known for working on children's programming such as LazyTown, Arthur, and Bump in the Night (the latter of which he co-created), and Warran Gaff, best known for his and Pontac's work together on the adult cartoon Happy Tree Friends. Pontac and Graff's renditions of Sonic were significantly more lighthearted than earlier or later 3D games, a highly requested shift at the time that would prove controversial after a few games. This disdain for Pontac and Graff's writing style led Pontac to decline from doing Sonic panels at conventions out of fears that vitriolic Sonic fans will visit and harass him.

The design for Dr. Robotnik/Dr. Eggman was based on a caricature of Theodore Roosevelt in pajamas.

In all of the Sonic Riders games, there is a gear titled "The Crazy", which resembles a taxi. This is most likely a reference to another SEGA series, Crazy Taxi.

Tails' real name, Miles Prower, is a pun on "miles per hour", a reference to Sonic's speed.

There is a series of posters in several Sonic games advertising a movie series called "Chao in Space". These posters also feature the names of various Sonic characters.

The trademark Sonic Emblem, as featured in Sonic the Hedgehog and subsequent installments on the Sega Genesis, is based off of the logo from the 1988 Sega arcade title, Wonder Boy III: Monster Lair.

In the early Sonic games, The Chaos Emeralds appeared to be 'Emerald Cut'. Eventually, the emeralds in the series became 'Brilliant Cut'. In reality they should now be Chaos Diamonds, as a brilliant cut is reserved for diamonds.

In the 1990 arcade racing game Rad Mobile, there is an air freshener of Sonic that is hanging from the rear-view mirror. This marks the first time Sonic has ever made an appearance in a video game, which, interestingly enough, predates the release of Sonic the Hedgehog in 1991.

In the continuity of Fleetway's Sonic the Hedgehog comics (known as "Sonic the Comic"), Dr. Robotnik was originally a kind human scientist named "Ovi Kintobor", who wished to rid Mobius of all evil using a device called the Retro-Orbital Chaos Compressor (or "ROCC" for short) to absorb all the negative energy on the planet, eventually using the six Chaos Emeralds as a vessel for the energy (Issue #181 would reveal that this was because the Drakon Empire had used them in the past to contain an experimental energy source known as "chaos"). However, six emeralds was not enough: he also needed the seventh Grey Emerald to stabilize the process. During this time, he met and befriended Sonic the Hedgehog, who used his impressive speed to help Kintobor in his search for the Grey Emerald, albeit to no avail (Issue #36 would reveal this was because the Grey Emerald was on the Floating Island with Knuckles). Kintobor would also run experiments on Sonic to test his speed, which eventually lead to him gaining his iconic blue form.

The day after this (according to Issue #71), when Kintobor went to go make them some food, he could only find a six month old rotten egg in the fridge. While going to add salt to the egg, he tripped on a cable and slammed his head against the ROCC's control panel, causing it to explode. Both Kintobor and the egg were bathed in chaos energy, transforming him into Ivo Robotnik, the main antagonist of the comic, and revealing that Sonic was responsible for "Creating the most vicious dictator on Mobius". All of this is revealed in Issue #8 of the comic.

Issue #71 revealed that the accident was actually caused by a time-travelling Sonic, who both placed the rotten egg in the fridge and pulled the cables loose. This was done to save the future from the Brotherhood of Metallix, who could only be stopped by Robotnik. Additionally, Issue #26 revealed that the explosion had somehow "burned" Kintobor's brainwaves onto one of the Golden Rings from which the ROCC had been built: it would later be used to construct the Kintobor Computer, an important part of the Freedom Fighters' resistance to Robotnik's rule.

In "Sonic the Comic, issue #8, The Origins Of Sonic," Sonic was originally a normal, brown, and very spiky hedgehog. He had met Dr. Ivo Robotnik (known at the time as Dr. Ovi Kintobor) by finding his lab, and they had become friends. Dr. Kintobor performed experiments on Sonic's super speed, which helped him to run even faster, and with the aid of the Power Sneakers Dr Kintobor invented, it allowed him to run so fast that he broke the sound barrier, turning him into a more familiar blue form.

In 2008, the series was awarded the Guinness World Record for the "longest-running comic series based on a video game". Archie Comics' run of Sonic the Hedgehog lasted from 1992 to 2016, resulting in the publication of 290 issues (including specials) over the course of 24 years.

In 1993, Sonic the Hedgehog became the first video game character to appear as a balloon in the Macy's Thanksgiving Day Parade. The balloon popped on it's one and only flight by being pushed into a lamp post by strong gusts of wind, hurting a kid and a police officer on it's descent. Because of this incident, the balloon was retired.

A second Sonic balloon based on his modern redesign was used between 2011 and 2013 to celebrate the series' 20th anniversary, and was brought back one more time in 2021 in accordance with the series' 30th anniversary.

Sonic's favorite food is chili dogs. This trait was first introduced in the 1993 animated series "Adventures of Sonic the Hedgehog" and was later officially incorporated into the video game series starting with Sonic Chronicles: The Dark Brotherhood. Before the first appearance of the chili dog in the series however, Sonic's enjoyment of hot dogs in general was first established in Issue #5 of "Sonic the Comic", in a scene where Sonic is seen ready to eat three hundred hot dogs as a part of his breakfast. Since then, the chili dog has been established as Sonic's favorite food in almost every piece of Sonic media (for context, the only show to not reference chili dogs was "Sonic X", and even then a normal hot dog appeared in the episode "How to Catch a Hedgehog" during a scene where Sonic is stuck running in a giant hamster wheel), eventually making its way into the games as well, a rare example of something originating from the cartoons/comics being carried over into the mainline games.

In 2010, SEGA de-listed every single Sonic game with anything less than an average Metacritic score so that they could not be bought new at retail or downloaded from console-based online services. This was in order to increase the value of the franchise to prepare for a "comeback". Ironically, Sonic Free Riders, released the very same year, has a below-average Metacritic score of 47 out of 100.

Sonic was originally planned to have a human girlfriend called Madonna. She would chase Sonic around, similar to how Amy Rose acts in later games.

Jon St. John, the voice of Duke in the Duke Nukem games, also voiced Big the Cat for several Sonic games starting with Sonic Adventure up until Sonic Heroes.

Sonic's shoes were inspired by Michael Jackson's boots and the color scheme of Santa Claus. Sonic's personality was inspired by Bill Clinton.

There are at least two cases of art plagiarized from deviantart.com appearing in Sonic games. A piece of art of Sonia was mistakenly added to Sonic & Sega All-Stars Racing, and some fanart that was made for a Sonic & the Black Knight contest turned out to be a replica of someone else's artwork. Sega apologized both times.

The human body has a Gene called "Sonic Hedgehog", named after the character. The gene has an inhibitor (something that stop the process of a gene) named "Robotnikinin", named after Sonic's Nemesis, Dr. Ivo "Eggman" Robotnik.