"Mutant" is one of the three first seminal Swedish role playing games, together with Drakar och Demoner and Chock.
The original Mutant was based on Basic Roleplaying System and was released in 1984. It was set in a post-apocalyptic future where most of the human race had been eliminated by a disease. The survivors hid away in subterranean enclaves and genetically experimented on humans and animals and sent them up above ground to see if they could survive. A following nuclear war between the enclaves eradicated humanity more thoroughly, technology was forgotten, and the only survivors were these humanoid mutants and humans in cryo-sleep. The country has now broken down into smaller societies, technology has been forgotten and is now on pre-industrial revolution level. But there are still the "forbidden zones", where lost technology still lies untouched but where the radiation levels are lethal.
"Mutant 2" was released as an expansion in 1986, and changed the die rolling rules to reflect those of Drakar och Demoner Expert, where the designers left Basic Roleplay and changed into a system based on icosahedric dice.
In 1989, "Mutant 2089", or "Nya Mutant" was released. Not only were there several rules changes, inspired by the cyberpunk wave, the setting was changed from a pre-industrial revolution technology society to large mega-cities, controlled by huge corporations. Designers suggested that the old Mutant setting existed in between these cities.
Mutant R.Y.M.D. in 1992 took another step from the basic setting and was more a space-travel science fiction roleplaying game. The ruleset was very similar to Mutant 2089 and the settings were officially compatible. This version was short-lived, though, as it soon was transformed into Mutant Chronicles.
Mutant Chronicles further enhanced the setting of Mutant RYMD, but added creatures and other ideas from the successful horror RPG "Kult".
In 2002, when Target Games has ceased to exist, another publisher called Järnringen published "Mutant - Undergångens arvtagare" (The Inheritors of the Apocalypse). With this, they reverted back into the first setting with a pre-industrial revolution setting populated by mutants and mutated animals. "Järnringen" (Iron Ring) was also the title of one of the very first scenario modules for the first "Mutant".
Järnringen ceased publication of "Mutant - undergångens arvtagare" in 2008, while continuing with their space travel RPG "Coriolis".