Who said "A man must do his duty."?

This quote is attributed to Jon Snow.

A man must do his duty. - Jon Snow

"A man must do his duty."

Jon Snow Work

"The things we love destroy us every time."

"I am of the night."

"The North Remembers."

"When the snows fall and the cold winds blow, the lone wolf dies, but the pack survives."

"Hard work never killed anybody."

"Work with purpose and integrity."

"Hard work pays off in the end."

"A man's gotta do what a man's gotta do."