Tom Clancy's Splinter Cell is a series of award-winning stealth video games, the first of which was released in 2002, and their tie-in novels. The protagonist, Sam Fisher, is a highly trained agent of a fictional  black-ops sub-division within the NSA, dubbed "Third Echelon". The player controls Fisher to overcome his adversaries in levels (created using Unreal Engine) that were extended to emphasise light and darkness as gameplay elements. All the console and PC games in the series were critically acclaimed, and the series is commercially successful. The series, along with Assassin's Creed, is considered to be one of Ubisoft's flagship franchises, selling more than 31 million copies as of 2011.