"Doom" is one of the most significant games in video game history, frequently cited as one of the greatest games of all time. Along with its predecessor "Wolfenstein 3D", it helped define the FPS genre and inspired numerous similar games, known as "Doom" clones. It pioneered online distribution and technologies including 3D graphics, networked multiplayer gaming, and support for custom modifications via packaged WAD files. Its graphic violence and hellish imagery also made it one of the top video game controversies in history.