For years it was only urban legend, but when the official Star Trek website does a full story on it, it has to be true.
Originally a death mask of William Shatner created for Star Trek, it became mass produced by Don Post Studios, and of course painted white for the iconic on-screen serial killer.
Just look at this vintage ad for the masks, and imagine the upper right photo with a large bloody knife in hand...
If that's not enough of a verification, check out this video from Shatner himself...
