1/ Maze Wars

How: Created by Steve Colley in 1973 who went on to work for NASA on the Mars Rover.

What: Not the hardest game in the world by any means. Players wander around a maze, only able to move backwards, forwards, right or left, and peeking through doorways. Other players are seen as eyeballs. When a player sees another, they can shoot them. Points are gained for shooting other players, and lost for being shot. Occasionally in some versions, a duck also appears in the passage. Obviously.

Special: This was historically the trend-setter for all future 3D-based games and graphic programs.

2/ Wolfenstein 3D

How: Created by id Software in 1992 for MS-DOS, you remember that? The thing Windows forces you to use after its weekly crap-out.

What: This follows the adventure of William "B.J." Blazkowicz, an American soldier of Polish descent on his attempt to escape castle Wolfenstein. The fight is against armed guards and attack dogs with only three different guns to do the job. Over ten levels were on offer in the shareware which was downloadable for free, the commercial version pushed that up to a more hearty sixty levels.

Geek 101: To render the walls in pseudo-3D, the game used ray casting, a special case of ray tracing. This technique sent out one ray for each column of pixels, checked if it intersected a wall, and drew textures on the screen accordingly, creating a one-dimensional depth buffer against which to clip the scaled sprites that represented enemies, powerups, and props. Essentially all working to let you kill Nazis. So good then.

Special: After the game was siezed in Germany in 1994 the Americans toned down their version removing swastikas, changing the blood for sweat and the attack dogs to large rats. Shooting rats and people is ok but not dogs...

3/ Doom

How: id Software do it again in 1993 with this smash hit on the PC. The shareware was downloaded by 10 million people within two years and this is before broadband speeds.

What: The player takes the role of a space marine, "one of Earth's toughest, hardened in combat and trained for action", who has been deported to Mars as punishment for assaulting a senior officer when ordered to attack civilians (Running Man much?). The Union Aerospace Corporation (UAC), a multi-planetary conglomerate, is performing secret experiments with teleportation between the moons of Mars, Phobos and Deimos. Standard. When the inevitable occurs and hell starts spilling out of the gates it's up to Mr. Marine to deal out the pain on each planet and finally in Hell. Featuring three chapters, each with nine levels (only one chapter in the shareware version) and with bosses like the Cyberdemon Lord and Spiderdemon, this game had it all. Now having migrated to flash you can play it online here.

Geek 101: The first game to have stereo sound. Unlike Wolfenstein it had height differences, non-perpendicular walls, weapon sway while moving, full texture mapping and varying light levels. This is what allowed the makers to give this game a far scarier atmosphere than its predecessor. Debatable, depending on your level of Nazi fear.

Special: Doom was voted by industry insiders to be the greatest game of all time in 2004. Here's one reason - the weapon selection: pistol, brass-knuckle dusters, chainsaw, shotgun, chaingun, rocket launcher, plasma rifle, and finally the immensely powerful BFG 9000. A first to 3D gaming was the berserk pack: a dark first aid box that puts the character into berserk mode, allowing them to deal out rocket launcher-level damage with their fists and potentially splattering former humans and imps, as well as setting the user's health to 100% if it was lower. Makes you feel like your're tough for a few seconds in your life.

The main thematic influences came from Aliens and Evil Dead II. The title of the game was picked by its maker John Carmack: "There is a scene in The Color of Money where Tom Cruse shows up at a pool hall with a custom pool cue in a case. 'What do you have in there?' asks someone. 'Doom' replied Cruse with a cocky grin. That, and the resulting carnage, was how I viewed us springing the game on the industry."

Doom remains notorious for its high levels of violence, gore, and satanic imagery, which have generated much controversy from a broad range of groups. Yahoo! Games has it listed as one of the top ten controversial games of all time.