Ka of Osiris
When Osiris absorbed the identity of Ptah, becoming Ptah-Seker-Osiris, the Apis bull became considered an aspect of Osiris rather than Ptah. Since Osiris was lord of the dead, the Apis then became known as the living deceased one. As he now represented Osiris, when the Apis bull reached the age of twenty-eight, the age when Osiris was said to have been killed by Set, symbolic of the lunar month, and the new moon, the bull was put to death with a great sacrificial ceremony.
There is evidence that parts of the body of the Apis bull were eaten by the pharaoh and the priests to absorb the Apis's great strength. Sometimes the body of the bull was mummified and fixed in a standing position on a foundation made of wooden planks. Bulls' horns embellish some of the tombs of ancient pharaohs, and the Apis bull was often depicted on private coffins as a powerful protector. As a form of Osiris, lord of the dead, it was believed that to be under the protection of the Apis bull would give the person control over the four winds in the afterlife.
By the New Kingdom, the remains of the Apis bulls were interred at the cemetery of Saqqara. The earliest known burial in Saqqara was performed in the reign of Amenhotep III by his son Thutmosis; afterwards, seven more bulls were buried nearby. Ramesses II initiated Apis burials in what is now known as the Serapeum, an underground complex of burial chambers at Saqqara for the sacred bulls, a site used through the rest of Egyptian history into the reign of Cleopatra VII.
The Apis was a god to be venerated for his excellent kindness and for his mercy towards all strangers. Apis was the most popular of the three great bull cults of ancient Egypt (the others being the bulls Mnewer and Bakha.) Unlike the cults of most of the other Egyptian deities, the worship of the Apis bull was continued by the Greeks and after them by the Romans, and lasted until almost 400 A.D.
Read more about this topic: Apis (god)