Nightcore is an artist. It is composed of two boys from Alta, Norway; Thomas S Nilsen (a.k.a. DJ TNT) and Steffen Ojala Søderholm (a.k.a. DJ SOS). The group was formed in 2002 and released five known albums of tracks with raised tempo and pitch. These albums were composed of purely electronic tracks with an emphasis on techno, trance, and dance music. However, the tracklistings of these albums are unknown and not all of the songs reached the Internet or were distributed past their hometown. Most of what was known about them can be pulled from their old defunct website, viewable through Wayback Archive: click here.
After 2003, the group disappeared. No news or releases came from them. The only information regarding them came from a fanmade MySpace page easily accessible through Google search. The Bio was copied from the group's aforementioned website before it went down. There was no known way to contact them. Years passed, and video-sharing sites such as YouTube sprung up. Tracks from the Nightcore group were uploaded on YouTube (it is unknown who first did), and steadily gained popularity. As these videos gained millions of views, Nightcore was "exposed" as having produced none of the tracks themselves, being mere speed edits (the group never openly admitted this). Anyone with basic sound editors could create songs exactly how Nightcore did.
So, that was what people started to do. Electronic (mainly techno, trance, and dance) songs were edited in Nightcore's "style" and uploaded on YouTube, being labeled as Nightcore songs. This practice still continues to this day, and YouTube is now home to tens of thousands of fan-made Nightcore songs.
Recently, in 2011, Nightcore has reappeared with the help of One Vibe Events, who sought them out to appear at a show in Phoenix, Arizona. Nightcore released a new single, Astral Plane and planned to play a new Norwegian song at this show. Unfortunately, Nightcore did not end up appearing at the show due to scheduling issues although, having returned, may appear at other shows in the future. They have an official Facebook page where they interact with their large fanbase that sprouted during the many years they were absent.