Mega Man 2, known in Japan as Rockman 2: Dr. Wily no Nazo (ロックマン2 Dr.ワイリーの謎?, lit. "Rockman 2: The Mystery of Dr. Wily"), is a platform game developed and published by Capcom for the Nintendo Entertainment System. It is the second installment in the original Mega Man series. The game was released in Japan in 1988, and in North America and PAL regions the following years. Mega Man 2 continues the titular protagonist's battle against the evil Dr. Wily and his rogue robots. The game features graphical and gameplay changes from the first Mega Man game, many of which have remained throughout the series. Although sales for Mega Man were unimpressive, Capcom allowed the Rockman team to create a sequel. They worked concurrently on other Capcom projects, using their free time to develop the game. Unused content from the previous title was integrated into Mega Man 2. Takashi Tateishi composed the soundtrack, with Yoshihiro Sakaguchi serving as a sound programmer. With more than 1.5 million copies sold, the game is the best-selling Mega Man title. Critics praised its audio, visuals and gameplay as an improvement over the first game. Many publications rank Mega Man 2 as the best title in the series, and as one of the greatest video games of all time. The game has been re-released on several consoles and mobile phones.