The mother of Hades and original leader of the Mutants, Karen Sawney Bean is apparently descended from Sawney Bean, a legendary Scottish serial killer and cannibal.

Karen originally lived in Yuma Flats with her husband Dan and their unnamed son, living, for the most part, a simple life. When the U.S. army attempted to buy Yuma Flats for nuclear testing, Karen, along with the rest of the towns inhabitants, refused to sell their homes. This refusal culminated in group of drunken soldiers returning to Karen's home in the night and forcing her and her family out on to the street. Made to watch as Lieutenant Ryan brutalized her husband and threatened her son, Karen witnessed Lieutenant Ryan accidentally shoot and kill Dan before fleeing the scene, though not before threatening Karen and her child.

Dan's death by soldiers apparently caused Karen to rally her neighbors into taking vengeance on the army, as the next day, several army personnel returning to Yuma Flats to try and re-negotiate with the people there, were killed or injured by snipers in an attack lead by Karen. This attack caused the army to retaliate against the people of Yuma Flats with extreme prejudice, as the next day they invaded with tanks. During this attack, Karen and her son were found and held captive in a dilapidated house by Lieutenant Ryan, who had lost a portion of his ear in the sniping attack. After killing Karen's son and beating her, Lieutenant Ryan was stopped from raping Karen by a superior officer, who restrained and reprimanded Ryan and freed Karen, who, while fleeing, stole Lieutenant Ryan's dog tags.

As Yuma Flats was destroyed and turned into a nuclear testing range, Karen, along with what was left of the inhabitants of Yuma Flats, lived in some nearby mines as atomic testing took place nearby. Acting as the leader of her fellows in the mines, Karen and them survived off supplies sold to them by a gas station proprietor named Jeb. It was sometime after the army finally stopped its nuclear testing that Karen and her people moved out of the mines and into the nuclear testing villages built by the military, it was also around this time that Karen discovered she was pregnant, despite not having sex since Dan had been murdered.

In the nuclear testing village, Karen still acted as leader, much to the resentment of a man named Patrick, who was suspicious of Karen's pregnancy. Karen eventually gave birth to a horrifically deformed son she named Hades, and whom she loved dearly despite his physical appearance. Having witnessed Hades' birth while spying on Karen, Patrick, disgusted by the child, who he was convinced was a bad omen and of Satanic origin, used intimidation to turn the townspeople against Karen. One night, Patrick confronted Karen with the townspeople and gave her an ultimatum--leave the town or be killed. Karen did leave the town, though not before killing and decapitating Patrick in revenge for threatening her.

Left to live in the mines with Hades, Karen and he were soon joined by others who had also given birth to mutant offspring and were driven from the town. After Jeb, who had been supplying Karen, became unable to sell anymore to her due to his business being strained, Karen made a deal with him; Jeb and his family would lure unsuspecting people into her and the Mutants' territory, where they would be killed and eaten, and in exchange, Karen would give Jeb any valuables they took from the travelers. After years of living like this, Karen eventually began to succumb to radiation poisoning caused by the nuclear radiation she had been exposed to years earlier. Becoming emaciated and bald, Karen, realizing her time had come, passed leadership of the Hill People on to Hades, telling him to keep her line alive (this, combined with the tribe almost becoming extinct following the army's purge, leads the mutants to adopt the policy of capturing, torturing and raping females until they fall pregnant and give birth to the mutants' offspring). After her death, Karen was buried in the makeshift cemetery passed through by Doug Bukowski in the first The Hills Have Eyes film.