Terror Is a Man (1959)

William Fitzgerald finds himself shipwrecked on an island whose native inhabitants have recently fled. His civilized host, the secretive Dr. Charles Girard, explains that they were superstitiously fearful of his scientific work. Now the only people on the island are the castaway, the scientist, his voluptuous wife, his sleazy assistant, his beautiful native servant and her young son. But there may be one more man on the island: it's all a matter of philosophy and semantics. It seems Dr. Girard is surgically transforming a panther into a human being. The trouble is, the creature is not above killing members of the species he has recently joined.