Dwight Frye's hunchbacked lab assistant in the first film of the Frankenstein series (1931) is the main source for the "Igor" of public imagination, though this character was actually named Fritz. Fritz did not originate from the Frankenstein novel, but instead originated from the earliest recorded play adaptation, Presumption; or, the Fate of Frankenstein, where he was played by Robert Keeley.
The second and third sequel films Son of Frankenstein (1939) and The Ghost of Frankenstein (1942) featured a character named Ygor (portrayed by Bela Lugosi). This character is neither a hunchback nor a lab assistant, but a blacksmith with a broken neck and twisted back as the result of a botched hanging. He reanimates the Monster as an instrument of vengeance against the townspeople who attempted to hang him for grave-robbing. He survives a near-fatal gunshot and appears in the next film in which his brain is placed in the Monster's body.
Universal Studios actively cemented the idea of the hunchbacked assistant to the "mad scientist" in the Frankenstein film series' The House of Frankenstein (1944) with J. Carrol Naish playing a hunchbacked lab assistant named Daniel.
In the horror film Mystery of the Wax Museum (1933), Ivan Igor is the name of the mad wax museum curator. The film was remade as House of Wax (1953), but the name Igor was given to the curator's henchman (Charles Bronson) rather than the curator himself. This character is deaf and mute, rather than a hunchback.