2. Pokémon - 175 million
Pokémon has spread from its humble beginnings as a turn based game on the Game Boy to feature in motion pictures, television series, trading cards, books and everything inbetween.
Taking its name from the Japanese for 'Pocket Monsters' the series revived Nintendo's Game Boy brand single-handled and is now omnipresent in popular culture. Just try finding a child over the age of six who doesn't know who Pikachu is or what a level 15 Bulbasaur does.