Ha' K'in Xook (Mayan pronunciation: [haʔ k’in ʃoːk]), also known as Ruler 6, was an ajaw of Piedras Negras, an ancient Maya settlement in Guatemala. He ruled during the Late Classic Period, from 767–780 AD. Ha' K'in Xook was a son of Itzam K'an Ahk II, and he ascended the throne upon the death of his brother, Yo'nal Ahk III. Ha' K'in Xook's reign seems to have ended either with his death or his abdication in favor of his brother K'inich Yat Ahk II, but archaeologists and Mayanists have not come to a clear consensus on this. Ha' K'in Xook left behind several monuments, including stelae at Piedras Negras and a stone fragment from El Porvenir. In addition, a stone seat known as Throne 1 which was erected by K'inich Yat Ahk II, records either the death or abdication of Ha' K'in Xook.