Celebrities endorsements have been around for a long time, but it's usually actors, wrestlers, or athletes who are enduring a photoshoot with a random product. That said, every now and again, it's a science fiction author who's promoting something.
By the 1980s, some science fiction authors had become bona fide household names: Isaac Asimov, Arthur C. Clarke, and others. This made them perfect spokesmen for a bunch of products outside of the usual science fiction fandom circles, but in markets where their names had some meaning to consumers.
Isaac Asimov was the face of Radioshack for a while, putting his science fiction credentials to work with the Tandy computer - it was part of an exclusive deal that would see him abandon his typewriter for a computer, something he wasn't thrilled with. He appeared in a variety of print ads for the company:
Asimov wasn't the only author to appear in advertisements: When Omni Magazine launched in the early 1980s, they had an enormous marketing budget behind them, allowing them to film a commercial (for a science fiction magazine!) with Arthur C. Clarke:
That's not the only time that Clarke appeared in an ad: a couple of years ago, BMW used the late author's voice to talk about the BMW i8:
Frank Herbert's novel Dune was a major hit with readers in the 1960s, propelling him into the public spotlight in the following years. This prompted Pacific Bell to put him before a camera and have him talk about the future and the upcoming internet:
Ray Bradbury appeared in his share of advertisements, including this bizarre one for Sunsweet Prunes:
He also appeared alongside Kirk Douglas in this Japanese commercial for Maxim Coffee:
Stephen King is probably the best-known speculative fiction author in the United States, and has appeared in a number of commercials over the years. In this one from SportsCenter, they make light of his work as a horror author and Red Sox fan:
King also also appeared in an ad for American Express in 1985:
More recently, he's appeared with IBM's Watson:
Finally, there's Harlan Ellison, who was inexplicably brought on to shill for the Geo Metro as a 'noted futurist' in 1988:
[h/t to Tobias Buckell]