Short answers, pulled from the story.
The Pyramid Texts date to approximately 2400-2300 BCE, making them the oldest known corpus of ancient Egyptian religious texts. They were carved into pyramid walls at Saqqara from the end of the Fifth Dynasty through the Sixth Dynasty of the Old Kingdom and into the Eighth Dynasty of the First Intermediate Period.
French archaeologist Gaston Maspero discovered the Pyramid Texts beginning in 1880 during excavations at Saqqara. He found hieroglyphic texts inside the pyramids of Pepi I and Merenre I, and by 1881 had also uncovered texts in the pyramids of Unas, Teti, and Pepi II.
The Pyramid Texts were funerary spells intended to transform a deceased pharaoh into an akh, a spirit form able to join the gods. The spells guided the pharaoh to the afterlife through every possible means, including climbing ladders, crossing by ferry, and flying, and could also summon or even threaten the gods for assistance.
Pyramid Texts have been found in the pyramids of pharaohs Unas, Teti, Pepi I, Merenre I, Pepi II, and Qakare Ibi, as well as in the tombs of queens Akhesenpepi II, Neith, Iput II, Wedjebetni, and Behenu. The oldest texts appear in the pyramid of Unas, the last pharaoh of the Fifth Dynasty.
The Cannibal Hymn refers to Utterances 273 and 274 of the Pyramid Texts, first appearing in the pyramid of Unas. It depicts the deceased king consuming the gods to absorb their divine powers, but scholars interpret the imagery as a metaphor for the king as the dawn sun absorbing the stars. Outside Unas' pyramid, only the pyramid of Teti also displays the Cannibal Hymn.
German Egyptologist Kurt Heinrich Sethe produced the standard concordance of the Pyramid Texts in German between 1908 and 1910. Samuel A. B. Mercer translated Sethe's work into English in 1952, and British Egyptologist Raymond O. Faulkner published a direct English translation in 1969 under the title The Ancient Egyptian Pyramid Texts.