Walter, the man in black, is the person Roland initially believed pushed Jake in front of the car and caused his death. He later decides that Walter wasn't the guilty party.... that it was Jack Mort. Roland is following Walter when he meets up with Jake at the way station. He later wakes up with Walter's dead body next to him. Roland takes Walter's jawbone as a token and keeps it with him until he throws it into the fire. Walter's jawbone burns and shows Eddie a vision of the rose and the key.
The Waste Lands