True Name
Explanation
The Joke
A person thanks a demon for a pleasant visit. The demon, before leaving, says he didn't catch the person's "true name" — which in fantasy and folklore lore is the name that gives someone complete power over another being. The person's companion immediately warns them not to reveal it, referencing that knowing someone's true name along with their date of birth and blood type gives "the opener complete power over" them. The demon says "I'll tell you mine first" and gives his name. The last panel reveals the punchline: "His name was 'Gerald.' Never be spoken."
The Humor
The comic plays on the classic fantasy trope of "true names" — the idea (found in fairy tales, demonology, and works like Ursula K. Le Guin's Earthsea series) that knowing a supernatural being's true name gives you power over it. The joke subverts this by making the demon's true name utterly mundane: "Gerald." The humor comes from the contrast between the ominous buildup about the terrifying power of true names and the anticlimactic revelation that this fearsome demon is just a Gerald.
There's also a secondary joke about how modern identity theft works similarly to the true-name concept — knowing someone's name, date of birth, and other personal details really does give people a kind of power over you in the modern world (access to accounts, credit, etc.).