The photo that was believed to be Jack Chick was really him. It was confirmed after he died, when Chick publications released more pictures of him. He did make small public appearances though. That’s how Catholic Apologist Jimmy Akin met him and drew the famous sketch of him that everybody remembers. Chick didn’t want pictures circulating because he thought that the Jesuits would assassinate him.

I’d say that the Simpson’s voiceover only kind of counts we count Greg Egan as making no public appearances. Egan interacts with the public, but he only does it in text online. I think he’s just a private person who doesn’t want to be recognized. So letting people hear your voice might make you recognizable? He’s about as famous as someone would be who 1) exists entirely within the genre ghetto and 2) is still around but was more popular in the ’90s and early 2000s. He’s had a solid international following for decades and publishes in the major SF magazines, used to appear nearly every year in “Year’s Best SF” collections, ect. That’s real success, but it’s not really “I can’t walk down the street anymore!” success. Maybe he has a phobia of stalkers or something.
The most likely way for someone like Egan to become really famous is to have a story optioned into an (almost certainly unfaithful) movie. By coincidence, I found out yesterday about the only commercial film adaption of one of his works, an episode of a shortlived Syfy Channel series called Welcome to Paradox. I watched a different episode of it, based on James Tiptree Jr.’s story The Girl Who Was Plugged In. It was awful. I mean…I seriously don’t know how much worse a faithful adaptation of that story could realistically have been. I will watch at least two more episodes of that series. The one with the highest IMDB rating stars Henry Rollins.