Hodor was a common person who lived in the realm owned by the Starks of Winterfell. He worked as a stable boy and had been a part of a family that had been in residence at the starts for generations. As a young boy hold or was stricken with an illness that left him and capable of speaking and severely limited his mental development. He would serve the Starks as a stable boy. Before being turned into a transport and protection system for young Brandon Stark. Hodor was kill feeling his mission to hold the door so Brandon Stark could escape and onslaught of white walkers. He may or may not be Undead himself.