Lon Chaney's horrific, self-applied makeup was kept secret right up until the film's premiere. Not a single photograph of Chaney as The Phantom was published in a newspaper or magazine or seen anywhere before the film opened in theaters. Universal Pictures wanted The Phantom's face to be a complete surprise when his mask was ripped off.
Gregory Peck's earliest movie memory is of being so scared by The Phantom of the Opera (1925) at age 9 that his grandmother allowed him to sleep in the bed with her that night.
When Rupert Julian was first presented with the script, he simply said "Lon Chaney, or it can't be done!"
According to the film's cameraman Charles Van Enger, one of Lon Chaney's most trusted associates, Mary Philbin's reaction to the unmasked Phantom was real - she had no idea what he would look like until that exact moment.