Who Erdnase was is one of the enduring mysteries of magic (illusion). Martin Gardner has proposed that a small-time con man named Milton Franklin Andrews was the author (S. W. Erdnase spelled backwards is E. S. Andrews, lending support to the theory that Andrews was the author's last name). Others argue against Andrews being Erdnase because the known examples of his writing are very much inferior to the polished writing of The Expert at the Card Table.
Some argue that Erdnase was probably a well educated, locally prominent individual, hiding behind an alias to protect his social standing. The most prominent individual mentioned in this regard is a mining engineer named Wilbur Edgerton Sanders, proposed by magician and private detective David Alexander.