In 1941, a Capelis XC-12 transport aircraft flown by pilot James "Mac" McCarthy (Dick Purcell) flying between Cuba and Puerto Rico runs low on fuel and is blown off course by a storm. McCarthy, unable to pick up any radio transmissions over the Caribbean, hears by a faint radio signal. After crash-landing on a remote island, his passenger Bill Summers (John Archer) and his black manservant/valet, Jefferson Jackson (Mantan Moreland) take refuge in a mansion owned by Dr. Miklos Sangre (Henry Victor) and his wife Alyce (Patricia Stacey).
The quick-witted yet easily frightened manservant soon becomes convinced the mansion is haunted by zombies, and confirms this with some of the doctor's hired help. With the help of Barbara Winslow (Joan Woodbury), the stranded group begins to find out what mysterious events are taking place in the mansion.
Exploring, the group stumbles upon a voodoo ritual in the cellar. It is being conducted by the doctor, who is in reality a foreign spy, trying to acquire war intelligence from a captured US Admiral whose aircraft had crashed in a similar fashion on the island. McCarthy comes under the doctor's spell but Summers comes to his aid. Information is being transmitted to Barbara, but Summers stops the ritual. The interruption causes the zombies to turn on their master. Sangre shoots the pilot but falls into a firepit and dies. With Sangre dead, all the zombies are released from the doctor's spell.
King of the Zombies was announced in January 1941 as a vehicle for Bela Lugosi. It was inspired by the success of The Ghost Breakers (1940).
Lugosi was meant to play the role of Dr. Miklos Sangre. When he became unavailable, negotiations ensued to obtain Peter Lorre for the part, but a deal could not be reached. Veteran character actor Henry Victor was signed just prior to the date of filming.
Principal photography by Sterling Productions, Inc. began on March 28 and wrapped early April, 1941, primarily filmed on a studio back lot. The transport aircraft used in King of the Zombies is the Capelis XC-12, built in 1933 by Capelis Safety Airplane Corporation of California. The aircraft was a 12-seat, low-wing cabin monoplane with two 525 hp Wright Cyclone engines.
In the press kit for King of the Zombies, Monogram advised exhibitors to sell "it along the same lines as Paramount's The Ghost Breakers (1940)." The Bob Hope horror/comedy was a runaway hit at the time.
Writing in The Zombie Movie Encyclopedia, academic Peter Dendle called King of the Zombies "... utterly absurd and delightful". Bruce G. Hallenbeck, who wrote Comedy-Horror Films, said that the film's politically incorrect humor comes off as innocent due to Moreland's delivery.
King of the Zombies was nominated for an Academy Award for Best Music (Music Score of a Dramatic Picture) (Edward Kay).
Two years later,King of the Zombies was followed by a sequel, of sorts, called Revenge of the Zombies (1943) that included two of the original cast members. Mantan Moreland reprised his role as Jeff. Madame Sul-Te-Wan was cast as Mammy Beulah, the housekeeper.