Heiankyo Alien (平安京エイリアン, Heian-kyō Eirian), known as Digger in North America,[2] is a maze video game created by The University of Tokyo's Theoretical Science Group (TSG) in 1979.

Over the course of two days, the group held meetings on the first floor of the student union building to brainstorm potential game ideas.

[7] The idea of the game was conceived by Itaru Kawakami, beginning as a game themed around the player laying down traps in a house to catch cockroaches — feeling that the idea gave the player too much free movement, it was revised to make the playfield resemble a Go board.

[7] The Go-like board was slightly tweaked to resemble a cityscape; after multiple real-world areas were suggested, such as Kyoto, Japan and San Francisco, California, the team ultimately decided to base it on the capital city of Heian-kyō, with the player being changed to a Heian period police officer.

[7] Not wanting their idea to go to waste, the group began programming the game on an Apple II computer, but it suffered from bad optimization and long load times.

[7] A candy power-up item that caused all aliens to stop moving for a brief moment of time, a homage to the Kuchisake-onna monster from Japanese folklore, was considered but later scrapped as it complicated the game's controls.

[7] The player's death animation, depicting an angel floating up off the screen, was made as a last-minute addition by request from Denki Onkyō.

[7] Heiankyo Alien was presented at the 1979 Amusement Machine Show held in the Harumi area of Chūō, Tokyo.

The game was also ported to the Super Famicom by Nihon Bussan in 1995 as Nichibutsu Arcade Classics 2: Heiankyo Alien.

In 2021, Mindware and exA-Arcadia released an enhanced arcade version of Heiankyo Alien 3671 titled Cosmic Digger 3671 in territories outside of Japan.

This version is playable with up 4 players simultaneously and compatible with both 4:3 and 16:9 monitors which completely changes the playfield in all generated stages.

[12] Many copied arcade versions of the game exist with differences in background color and sound effects.

Heiankyo Alien was an early example of a maze chase game, predating Namco's Pac-Man (1980).