"Los' cannot die," Femalo said, as if explaining something obvious to a three-year-old. "And you-"
"You poor saps-" his partner put in with good-natured viciousness.
"You can't kill a man who's already dead," Fimalo finished. "As he was, Roland, your guns might have ended him..."
Roland was nodding. "Handed down from father to son, with barrels made from Arthur Eld's great sword, Excalibur. Yes, that's also part of the prophecy. As he of course would know."
"But now he's safe from them. Has put himself beyond them. He is Un-dead."
- The Dark Tower page 608