At King's request, the only people who knew that he was Bachman were his editor and publisher, and, in every other sense, it was to be treated like some unknown hack writer's first novel. That meant as little promotion as possible -- just throwing it out into the discount section of a few bookstores and seeing what would happen.
And because King doesn't do anything by half measures, he invented an entire backstory for Bachman to satisfy the curious: He was a former marine who now lived on a dairy farm with his wife Claudia, and they had lost a child due to a tragic accident. He even went as far as to include a fake photograph of Bachman, which was actually a photo of the insurance agent of King's agent, Kirby McCauley:
Claudia Inez Bachman
Seen here about to ask you if you want to go hunting, drink whiskey, and talk about life's greatest mysteries.
"Bachman" wound up publishing five novels, which sold poorly at first but gradually began to develop a cult following. As a result, the fifth book, Thinner, was a minor hit, and an unsuspecting reviewer actually described it as "what Stephen King would write if Stephen King could write."
One fan of "both" authors became suspicious enough to investigate and wound up discovering that the Library Of Congress listed King as the copyright holder to Bachman's novels. King gave up the game without a fight and dropped the Bachman charade (although, he would later release another two books as Bachman, presumably just to spite that one critic with his sweet burn.)