Sonic the Hedgehog 2 (ソニック・ザ・ヘッジホッグ2 Sonikku za Hejjihoggu Tsū?) is a platform video game developed by Sonic Team and Sega Technical Institute, and published by Sega. The game is an installment in the Sonic the Hedgehog series, and focuses on the protagonist Sonic the Hedgehog and his friend, a fox named Miles 'Tails' Prower, who must stop the series antagonist Dr. Ivo Robotnik from stealing the Chaos Emeralds to power his Death Egg space station. Originally released for the Sega Genesis/Mega Drive in 1992, the game was a critical and commercial success, with critics praising it for building upon the original Sonic the Hedgehog game. The game has sold over 6 million copies, making it the second-best-selling game on the console, behind only its predecessor in the Sonic series. Since its initial release, the game has been released in several compilations and download releases for various platforms, which were also generally positively received.