Above: This picture is from the Papyrus of Hunefer, in the British Museum. Osiris is sitting on his throne, on a pool of water. He is dressed as a mummy and wears the white crown of Upper Egypt with two big feathers. He holds the symbols of authority, the crook and the flail. His skin is green because of his association with resurrection - that is, growth of new life, like plants after the flood.
From the water comes a lotus plant, and standing on the flower are the four sons of Horus (who was the son of Osiris).
Osiris was the main god of the afterlife. When a person died he was believed to be resurrected in the form of Osiris. It was therefore important for a person to be buried looking as much like Osiris as possible.
Osiris was also the god of fertility. Egyptians prayed to him to make sure the crops grew well. Each year the Nile flooded, which left the soil very fertile.
Right is a picture of Osiris from the tomb of Sennedjem in Luxor. Before him is an incense stand with lotus flowers.
The Myth of Osiris
Osiris was worshipped at Abydos. Every year there was a festival in which his myth was reenacted, like a play. Here's the story, as told by the Roman writer, Plutarch:
Osiris was once the king of Egypt. He ruled well, and made his evil brother Seth jealous. Seth secretly found out the measurements of his brother's body, and had a magnificent casket made for him. He then organized a banquet, to which he invited 72 accomplices, as well as Osiris.
During the feast Seth brought out the coffin and said whoever could fit in it could have it has a gift. Osiris stepped inside, and was immediately locked in. The coffin was thrown into the Nile and drifted to the city of Byblos (in Lebanon) where it got stuck in a pine tree.
Osiris' wife Isis then rescued the casket and brought it back to Egypt. She hid it in the marshes, and prepared for a burial. But while she was away, Seth found the casket. He angrily cut up Osiris' body into 14 pieces, scattering them throughout Egypt.
Isis then searched for all the pieces and buried each in the place it was found. Now the body was put back together into the form of the first mummy, from which Isis conceived her son Horus.
The Contendings of Seth and Horus
In another myth, Horus fought Seth to avenge his father. These struggles lasted 80 years, until at last Osiris was declared ruler of the underworld and his son was made ruler of the living. Seth was left to rule the deserts.
Bronze Osiris statue, Bolton Museum