13 Things You Didn't Know About Friday The 13th
7. The Killer Was A Man Until The Very End
In Miller's original script, the killer terrorising Crystal Lake is referred to as 'The Prowler' for convenience’ sake. Betsy Palmer was only there to film for ten days, and was not available to shoot the initial scenes of the movie - she herself acknowledged that a man played the killer throughout the rest of the film until Mrs Voorhees reveals herself at the end.
The hands, feet, and trousers legs usually belonged to special effects legend Tom Savini's assistant, Taso Nicholas Stavrakis, now a minor legend in horror as a stunt performer and actor. He's known for playing the most zombies out of anyone in a Romero movie (five in Dawn Of The Dead and four in Day Of The Dead), as well as a non-undead role as one of the maniacal Rhodes' soldiers.
However, Stavrakis refused to come back for Friday The 13th Part 2 because Tom Savini had declined.