Osiris is an Egyptian god of fertility, regeneration of the Nile, agriculture and vegetation. But, especially after the myth of his death and resurrection, Osiris became a god of death, resurrection and judgment on the souls of the deceased.
For these reasons the aforementioned myth is the cornerstone of Egyptian eschatology and the birth of the moral role of the Egyptian religion, since it is where the ideas of good (personified in Osiris), of evil (personified in Seth), of the resurrection of divinity and its triumph over evil and death, and of the establishment of that divinity as an instance of judgment in relation to the destiny of man after death.
The myth tells that it was the kind and wise Osiris the king (in mythology, not in reality) who civilized Egypt by teaching men agriculture, establishing just laws and making them worship the gods, thus creating a religion. All without resorting to the force of oppression.
After finishing his work, Osiris left to teach his teachings to other countries, leaving Isis as regent of Egypt. However, when Osiris returned, his envious brother Seth and 72 of his companions locked Osiris in a chest in his form, then cast him into the Nile to drown. Fortunately Isis he looked for the chest and found it, bringing it back, although it did not help him much because Seth found the chest, took the body of Osiris and cut it into pieces that he scattered throughout Egypt ...
Without giving up, Isis put the body back together and brought Osiris back to life, having with him a son through magic, since he had found all his pieces except the penis. That son was Horus, who after avenged his father's death, overthrowing Seth and taking command of Egypt.
Osiris, despite being resurrected, could not return to the world of the living and went to the underworld, becoming the judge of souls and the sovereign from beyond. That is why, in the religious interpretation of the myth, the living pharaoh identifies himself (symbolically) with Horus and, at his death, with Osiris (symbolically also), in whose form he is worshiped.
Although on an even more general level, Osiris is a symbol of immortality and resurrection and that is why at a certain stage in ancient Egypt all the dead were transformed into Osiris.
Finally, in general, Osiris is represented mummified, with green skin, a staff, a whip or scepter and a crown; or, in its animal form, Osiris appears as a crocodile, a large fish, a dog, a heron or a black bull called the "Bull of the West", this title that expresses his reign in the underworld since the West is an Egyptian symbol from beyond.