Ra was born in an egg floating on the water, he got bored of doing nothing therefore, became the sun. He created a wife along with many gods and goddesses. He loved all of his children but he especially loved Osiris which is why he made him the first pharaoh of Egypt. Osirus took the throne alongside his wife Isis and his son Horus.
Set, Osiris' brother, felt deeply angered by hin becoming pharaoh and decided to kill Osiris and chop his ruins into the Nile river so that he would not be caught. Word spread and there were many theories of Set being the murderer. When Ra heard about this he gave the most important job of all to Osiris, the ruler of the land of the dead.
Once Horus had heard of the death he immediately tracked down his uncle Set and killed him.
Although Isis was happy for the revenge of her Osiris' death, she knew that she would never see her beloved husband again. Each year Isis returns to the Nile river and her sorrow, over the death, is what causes it to continuously flood.