Osiris is one of the most prominent gods of the Ancient Egypt, usually depicted as a mummified king, complete with the ceremonial curved beard, crown, flail, and crozier. His skin is generally green or black, to represent his association with the dead.
Once he took form and lived upon the earth, his brother, Set, murdered him out of either jealousy or rage and scattered his remains across Egypt. Ra took pity to his death and sent Anubis to prepare for the first ever mummification, however, the ritual is not sufficient to bring him back to the world of living. Instead, he stayed in the underworld to oversee judgments for the deceased.
The deceased had to be judged at the hall of judgment with their heart weighed against a feather; Osiris will welcome the deceased into his world if they are considered "'balanced."
Osiris represents the belief in rebirth and their feeling that order and justice preserved beyond the gave.