The Answer
Frankenstein’s monster has no name.
The films in the first half of the 20th century are largely responsible for leaving people with the impression that the monster’s name was Frankenstein.
By now, I think everybody has been corrected enough times to know that Frankenstein was the scientist in Mary Shelley’s groundbreaking horror novel rather than the monster. That raises the question of what the monster was actually named.
The short answer, as noted above, is that the monster was never named given an name in the novel. However there some names attributed to the monster by characters in the story, and in later adaptations.
In the novel
Fandom.com suggests that Frankenstein’s monster refers to himself as “Adam of your labours” when speaking to his creator. However, further investigation reveals that this may not be accurate. A search of the text of the book in the Gutenberg project finds no results for the name Adam. Even so, the phrase uses “Adam” as a metaphor rather than a name.
He is referred to by others as “ogre”, “devil”, “thing”, “creature”, “fiend”, and “wretch” among other things. None of these could be reasonably described as his name.
In stage productions
Not long after Frankenstein was written, the novel was adapted for the stage. Shelley herself made it clear that she intended for the monster to have no name.
Mary Shelley herself attended a performance of Presumption, the first successful stage adaptation of her novel. “The play bill amused me extremely, for in the list of dramatic personae came _________, by Mr T. Cooke,” she wrote to her friend Leigh Hunt. “This nameless mode of naming the unnameable is rather good.”
In film
The first major production of a Frankenstein film was the 1931 Universal Pictures movie starring Boris Karloff. Even though Karloff was credited as having played “The Monster”, the name Frankenstein quickly became associated with the now-familiar image of Frankenstein’s monster. The poster shown here definitely could be seen to suggest that Frankenstein was the monster.
Following this was 1935’s The Bride of Frankenstein. Since the bride was presumably a mate for the monster, not the scientist, it sure sounds like they’re saying the monster’s name is Frankenstein.
Dean Koontz’s Frankenstein Novels
Horror writer Dean Koontz released a series of novels that depict Frankenstein’s monster from the original Shelley novel, set nearly two centuries later in modern-day New Orleans. In this series, the monster has given himself the name Deucalion.
Deucalion in Greek mythology is the son of Prometheus. This is in reference to Victor Frankenstein seeing himself as a modern Prometheus. The full name of the original novel is Frankenstein; or, The Modern Prometheus.
There doesn’t seem to be anywhere else that uses this name and since the Dean Koontz novels can’t reasonably be considered authorized sequels to the original novel, we can dismiss this as a valid name (though it kind of makes sense).