Commando was an overhead 2D vertically scrolling run and gun arcade game developed by Capcom and released in 1985. For a time, this style of game was as popular as the 2D platform genre. The arcade game was ported to a large variety of home systems including the Atari 2600, Atari 7800, NES, Intellivision and various home computers including the Commodore 64. Interestingly, an Atari XE version was planned and completed but never released but the prototype was eventually discovered.
The Commodore 64 version is the one I am most familiar with. It is a very good example of the genre and quite good on the Commodore 64 though I always thought it was overly difficult. The music is unique on the Commodore 64 and the best of any version.
Nowadays, the arcade version is available in various collections and also appeared on the Wii Virtual Console and on Capcom Arcade Cabinet for the PS3 and Xbox 360. Still, the Commodore 64 version is worth a try even if just for the music. Tracking down an original disk and working system and disk drive is probably too much of a pain for anyone that doesn't already have one but emulation is always an option.
There were a number of sequels of sorts over the years. Mercs was the first true sequel and it was released in 1989. Commando 3 was also released as a downloadable game via Xbox Live Arcade and the PlayStation Network in 2008. Bionic Commando was also marketed as a sequel outside of Japan but it wasn't really intended as such. Also, the game Duet by Elite Systems, developer of the home computer ports of Commando, was first called Commando '86 and then Commando '87 though it isn't an official sequel.
All images above refer to the Commodore 64 version.