"Did you know a young boy drowned the year before those two others were killed? The counselors weren't paying any attention... They were making love while that young boy drowned. His name was Jason. I was working the day that it happened. Preparing meals... here. I was the cook. Jason should've been watched. Every minute. He was... he wasn't a very good swimmer. We can go now, dear." - Mrs. Voorhees talking about Jason Voorhees
Jason Voorhees was born on June 13, 1946 to Elias and Pamela Voorhees. He was afflicted with severe facial deformities, Hydrocephalus, an abnormally large head, and mental disabilities. Raising Jason on her own, Pamela kept her son isolated from the community, not letting him attend school and educating him in their home on the outskirts of Crystal Lake.
In the summer of 1957, Pamela, unable to get a babysitter for Jason, resorted to bringing him to Camp Crystal Lake where she worked as a cook. Jason had actually been with his mom most of the time instead of other kids, leading to them thinking he wasn’t very smart, so they started bullying him. While being bullied by the other campers, Jason attempted to escape from his tormentors, but the cruel children caught up to him on the dock and threw Jason into the lake where he drowned. The counselors were supposed to be watching the children, but instead were talking and having sex in the woods.
After surviving his apparent demise, he inhabited inside crude shelterin the forest, seemingly waiting for his mother to find him and managing to live in the woods surrounding Camp Crystal Lake for over 20 years. He lived off the land and whatever he could pilfer from the camp or other parts of civilization. During these years, Pamela never found out where he was, nor did they see each other again until her death.
After his mother's murder-spree, Jason, having witnessed his mother's death, grabbed her sweater, pants, severed head, and the machete that killed her and returned to his shack with them, placing the objects on a crude altar he had constructed as a shrine to his beloved mother. Two months after Pamela's death, Jason began his killing spree, starting with the one who killed his beloved mother. The only thing stopping Jason at this time were a few major injuries before Tommy Jarvis killed him.
Years after Jason's death, Tommy would be haunted by hallucinations of Jason, leading him to go to Jason's grave to try to destroy his body. However, something goes wrong and Jason's corpse is resurrected in a fashion similar to Frankenstein's Monster, which allows Jason to continue his rampage after death.