Tee-Hee.
Well, Annie Sprinkle claims (with some justification) to have invented the job, but it's a complex history. Before there were fluffers, there were de-fluffers. When I worked in the business there were a lot of places where the police would allow simulated sex, but no penetrations. In part that depended on what might happen if a case got to the U.S. Supreme Court, because one justice, Potter Stewart, had his own definition of obscenity which did not include simulations.
That could be hard (pun intended) on male actors. As discussed in The Other Hollywood by Legs McNeil and Jennifer Osborne*, when doing simulated sex it was a good idea to have a girlfriend around. In the very early 1970s a videographer who made simulated sex loops "discovered" deep throat technique when the actor had to take a break and get his hard-on softened by his very eager girlfriend. The photographer was so impressed with her style that --er-- shortly thereafter she did him, his roommate, and a friend of the roommate, a guy named Chuck Traynor, who happened to have a girlfriend who used the stage name "Linda Lovelace".
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*--I just have to say that I am hopelessly in love with Jennifer (from afar). She wears glasses, is very, very smart, has admirable boobage, and in person projects a kind of nerdly sexuality that makes me hot.