The hulking mass of a man they call Hodor (even though his real name is Walder) is considered mentally inept by every character he meets in the fantasy world George R. R. Martin built because he can only say one word, but what’s really going on in that giant, meaty head of his?
According to neuroscientist Indre Viskontas he may actually be suffering from expressive aphasia- “a neurological condition usually caused by a localized stroke in the front of the brain”, which leaves him with relatively normal comprehension but reduces his power of speech to just one word.
It’s a fascinating theory, but I’ll stick to my own theory that he’s looking for his missing dog Hodor and won’t stop saying his name until he’s found!