Sonic the Hedgehog is a 2 episode OVA (original video animation) which was originally pitched as a pilot for an animated Sonic the Hedgehog series. It was published directly to video, not being screened in theatres in either JP or NA. The episodes are titled as "Welcome to Eggmanland" and "Sonic vs Metal Sonic" when released seperately.
Most fondly known as "the Sonic OVA", it was released in North America in 1999, 2 days before to the release of Sonic Adventure and the Dreamcast. The Sonic OVA is known for its music, and the very interesting take on Sonic's world, prior to there being an established "Earth" in Sonic Adventure.
Legacy and References in Other Media
The Sonic OVA was released in Japan for audiences to rent in January 1996. Chaotix on the 32X was the newest mainline Sonic game released at the time, and Sonic Adventure wouldn't be released on Dreamcast until 1998.
As for North America, the Sonic OVA released on September 7, 1999, two days before the release of Sonic Adventure. Although I don't think the two stories interfere with each other too much. Simple things like Tails being an inventor and having some type of workshop in a tropical environment, Sonic's plane the Tornado also makes an appearance in both medias, Knuckles being some kind of treasure hunter, old and abandoned ruined eras, and humans are all things both present in the OVA and Sonic Adventure.
Story elements from the Sonic OVA have been referenced of the years, such as in IDW Sonic's sidestory, Scrapnik Island, where Mecha Sonic has fallen into a hot area and smacks away Sonic's hands similar to Hyper Metal Sonic had done to him in the OVA. Thankfully, Mecha Sonic's fate was different than Hyper Metal's and he was saved by Sonic and his fellow Scrapniks. Another reference from the Sonic OVA is Mecha Knuckles wearing Knuckles' hat from the OVA.









