Space invaders is an arcade game created by a man named Tomohiro Nishikado released in 1978. Initially, the game was called Space Monsters but then changed to space invaders by Nishakado's superiors. Nishakado spends a year designing and developing the hardware necessary to make the game a success. He went through a variety of moving enemies such as, tanks, combat planes and battleships, but refused to use humans as targets since he felt it was immoral to shoot them. Eventually, he drew inspiration and came up with bitmap images we know today looking like squids and crabs.
After releasing in Japan, the game quickly gained popularity earning over $600 million the first year in Japan alone! It was so popular that when it came to North America the doctors identified a condition called "Space Invaders Elbow"1 while a physician in The new England Journal of Medicine named a similar ailment the "Space Invaders Wrist"2.
Space invaders are one of the earliest shooting games created. It's also pretty straight forward the point of the game is to use hand-eye coordination to defeat all the alien invaders with a laser cannon while earning as many points as possible. There are five rows of eleven aliens (depending on the version) they move horizontally back and forth across the screen as they move towards the bottom of the screen closer to you. As the aliens are defeated they start to move faster along with the music bringing wave after wave of more difficult opponents, but watch out the aliens are known to shoot back. The only defense you have is the several stationary defense bunkers and your ability to shoot enemies down.
1"The Video Game Invasion: What Is It Doing To Children?". The Herald Journal. December 18, 1981. Retrieved March 5, 2012.
2 Forester, Tom (1988). High-tech society: the story of the information technology revolution (1st MIT Press paperback ed.). Cambridge, Mass.: MIT Press. p. 155. ISBN 0-262-56044-5.