The Ruger MK II is a rimfire

Rimfire ammunition

A rimfire is a type of firearm cartridge. It is called a rimfire because instead of the firing pin of a gun striking the primer cap at the center of the base of the cartridge to ignite it , the pin strikes the base's rim....

 single-action semi-automatic pistol chambered in .22 Long Rifle

.22 Long Rifle

The .22 Long Rifle rimfire cartridge is a long established variety of ammunition, and in terms of units sold is still by far the most common in the world today. The cartridge is often referred to simply as .22 LR and various rifles, pistols, revolvers, and even some smoothbore shotguns have...

 and manufactured by Sturm, Ruger & Company

Sturm, Ruger

Sturm, Ruger & Company, Incorporated is a Southport, Connecticut-based firearm manufacturing company, better known by the shortened name Ruger. Sturm, Ruger produces bolt-action, semi-automatic, full-automatic, and single-shot rifles, shotguns, semi-automatic pistols, and single- and double-action...

. Ruger rimfire pistols are some of the most popular handguns made, with over three million sold.
The MK II ("Mark Two") was made from 1982 to 2005. Previous models include the Standard, Ruger's first model, made from 1949 to 1982, and the MK I Target, made from 1951 to 1982.