For reasons known only to MGM, Boris Karloff, prominently featured in a key supporting role, is not credited on screen, but his name is more sensibly listed in ninth credited position in the Variety review of 16 October 1929. The likeliest explanation is that all the actors are billed according to their respective "groups," but since Karloff was not in any of them, he was simply overlooked when the credits were being prepared.
Like many films created during the initial wave of talking pictures, The Unholy Night (1929)was released in both silent and talking versions.
Director Lionel Barrymore, whose career began to take off in the sound era, was considered an innovator in the early talkie genre, inventing (simultaneously, along with several other industry figures) an emancipating sound boom. He was also notable for not going overboard with the fresh novelty of sound with the kind of constant music and chatter that marred some productions, and instead allowed silence to also intrude in his films when necessary.
The Unholy Night (1929) was written by Ben Hecht based on his short story originally titled The Green Ghost; it was only his second film credit after Underworld (1927). Hecht's initial ambition was to become a novelist, but his success writing for the theater and movies lured him to Hollywood. Hecht was a friend, not only of Lionel Barrymore, but of his younger brother John Barrymore and sister Ethel Barrymore.
The Unholy Night (1929) was Boris Karloff's second talkie following Behind That Curtain (1929). Lionel Barrymore had first cast Karloff as a sideshow mesmerist in The Bells (1926), Karloff's first film containing horror elements. Barrymore offered Karloff a slightly larger role as the Hindu servant Abdoul in The Unholy Night. But such small parts, performed well, were not the needed career-boost for Karloff. Already in his 40s, Karloff said he had stopped writing home because 'I had nothing to write about.' Nevertheless, Karloff enjoyed working with Barrymore and in the biography The Barrymores: The Royal Family in Hollywood, recalled that "In those days, it took several hours to light a set and Lionel would use this time to help me and other players improve our scenes...When I played my big scene, finding my dead wife, I realized Lionel had analyzed the scene inside out and given me hints that enhanced my own interpretation."