Sonic Team began development of the game in 2006, after having begun work on the core technology, the Hedgehog Engine, in 2005. The title was first brought to public attention when the Sonic Unleashed name was trademarked by Sega on March 12, 2008. Screenshots of cut scenes, artwork, and a video were leaked ten days later, with the title then officially confirmed by Sega on April 3, 2008 with a small selection of screenshots and an updated video. The game was developed internally by Sonic Team in Japan. It was originally intended to be the third installment of the Sonic Adventure series and subsequently, at an early development stage, had the working title Sonic World Adventure, complete with work-in-progress logo. However, the development team began to introduce enough new innovations to separate it from the Sonic Adventure titles, and so a new title, Sonic Unleashed, was decided upon. It was then later revealed that the game's name in Japan would in fact remain Sonic World Adventure for its release there.