A Game of Thrones discussion forum in 2008 (before the HBO show's premiere, so more accurately an A Song of Ice and Fire discussion forum) popped an obvious question: "What does Hodor Mean?" Warning: spoilers. If you watched episode five of season six, you know that question finally got answered in 2016. But in 2008, a user named Myrddin gave it his best guess:
The poor guy is just asking someone to hold the door for him, since he's always carrying someone else around. After a while, "Hold the door" became "Hold the doorHold the doorHoldoorHodoor. Dammit! Hold the door!" His mind finally snapped, and now all he can say is Hodor.
People say there's truth in comedy. People don't say there's comedy in old Internet discussion boards, but Myrddin's rather lame, offhand joke turned out to be almost completely true. At least as far as the phrase, "hold the door" is concerned.
As Bran warged into Hodor in the past, he caused him to hold a door just bursting at the seems with undead killers in the present, and past Hodor got warped by the experience—shouting "hold the door!" over and over until it became "hodor."
No one deserves to have their fate guessed at correctly by a wiseass on an ASOIAF forum, but Myrddin made it happen for Hodor.
RIP the giant man.