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 of black, to represent his association with the dead. Once he took form and lived upon earth, his brother Set murdered him out of either jealously 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 work of the living, instead he stayed in the underworld to oversee judgements for the deceased.
The deceased had to be judged at the hall of judgement with their heart weighed against a feather. Osiris will welcome them into his world if they are considered "balanced".
Osiris represents the belief in rebirth and their feeling that order and justice preserved beyond the grave.