Jason Voorhees, the son of Pamela Voorhees, was born deformed. He lived with his mother at Camp Crystal Lake (his mother was the camp cook), in the city of Crystal Lake. Jason was bullied incessantly until, in 1957, he tried to prove to the bullies that he could swim and drowned in Crystal Lake.
One year later two of the Camp Crystal Lake counselors were murdered and the camp was shut down. Future attempts to reopen the camp were plagued with problems, including poisoned water and unexplained fires.
In 1980 eight new counselors planned to reopen the camp, but ultimately all but one of the new counselors were murdered. The killer is ultimately revealed to be Pamela Voorhees. Pamela is then beheaded by the only survivor, Alice.
The very next year Alice is murdered by an unseen killer in her home. Five years after Alice's murder a group of counselors return to Camp Crystal Lake for training, and all but 2 are murdered (though one of the survivors cannot be found). The killer turns out to be Jason Voorhees. Full grown and seemingly indestructible, Jason kills to avenge his mother's death and to carry on her quest to keep the camp closed.
In each new incarnation Jason returns to be an unstoppable killer, only to be "killed" then later resurrected.