Steve Martin is LDS
This has got to be the most classic LDS legend. The oldie, but goodie, Steve Martin is a member. Sometimes it goes on to say that he has been seen wearing a CTR ring or reading the Book of Mormon. Usually, the legend includes that he has been baptized, but keeps it secret.
This story is untrue. Steve Martin is not a member (or is super, super secretive about it for you conspiracy theorists). Several years ago, a BYU Daily Universe journalism student tried to trace this story back to its origins and did find that a missionary did baptize a Steve Martin, but it was not THAT Steve Martin.