Osirians are a humanoid culture that resides on O'Cyris IV. There are actually several species of Osirins, one resembling humans, which make up the majority of the population, one resembling the Egyptian god Anubis, which are used as guards, and certain elite spiritual leaders, similar in appearance to the Egyptian god Thoth.
The Osirians claim to have visited Earth's ancient Egypt and taken inspiration from their culture and technology, such as preparing their dead "so as to scare Abbott and Costello." They also claim to have learned space travel from them, so we can infer that the Egyptians must have visited O'Cyris IV first, and then brought the Osirins with them to visit Earth.
The Osirians hold slaves, including the Australian Man in his second appearance, and force them to construct monuments to their pharaohs, which have included Anopsis, Cleotut, and Hamenthotep, the current pharaoh at the time of the Planet Express crew's arrival.
All decisions made by the ruling class are based upon the Wall of Prophecy, a fact which Bender exploits to his advantage.