Finally we have the answer to why Hodor only says ‘Hodor’ and it turns out that it is not a show-exclusive explanation. In the ‘Inside the Episode’ segment, showrunner David Benioff explains that this major twist came from the original source i.e. George R.R. Martin himself:
“We had this meeting with George Martin where we’re trying to get as much information as possible out of him, and probably the most shocking revelation he had for us was when he told us the origin of Hodor and how that name came about. I just remember Dan and I looking at each other when he said that and just being like, ‘Holy s–t.'”
The origin and repeated use of ‘Hodor’ is a result of Bran’s time travel when the Three-eyed Raven takes him back to Winterfell. The Three-eyed Raven gets killed by the Night’s King in the present, leaving the Stark kid alone in the vision. Meanwhile, Bran also wargs into Hodor in the present to help them escape the cave. Meera then yells at Hodor to ‘hold the door’ giving herself and Bran more time to escape from white walker attack. Bran stands in the past as a channel to the present, and the young Hodor (Willis) hears the words ‘Hold the Door’ and goes into a seizure, repeating the words ‘hold the door’ until he could just say a combination of three- ‘Hodor’. Dan Weiss explains:
“It was just one of the saddest and most affecting things. Even sitting in a hotel room having someone tell you this was going to happen in the abstract in some way and that ‘hold the door’ was the origin of the name Hodor, we just thought that was a really, really heart-breaking idea.”
To make the matters worse, Hodor dies while holding the door in the present, indicating that Bran’s presence during his death caused Willis’ seizure in the first place. How these events will play out in the upcoming book (The Winds of Winter) is still a mystery but at least it’s a confirmation that the origin on Hodor is what George R.R. Martin planned 2 decades ago, when the first book in the A Song of Ice and Fire series came out in 1996.
Rest in Peace Hodor!