The ancient Egyptian believed in different gods, even when one of their Pharaohs (Akhenaton) called for the worship of only one god (Aton), they followed his religion but kept their respect for other gods as well. Two of the most famous Egyptian Gods are Isis and Osiris, whose name means "the Strength of the Eye" and different other meanings. They were married and Osiris was the king of Egypt but also considered a god of the earth, so he was a god-king who was believed to have given Egypt civilization, he taught people about art, agriculture, religion, and law. He was kind and giving to his people, and he traveled to different places around the country to teach the natives, while leaving Isis as his regent to take care of people.
But that upset some people who wanted the citizens of the country to stay ignorant and poor, and so they got him killed, and that is how he came to be the god of the dead, and the king of the afterlife. The main force behind the people who killed him was his brother Seth, who wanted to acquire both the throne and Isis, and he succeeded in killing Osiris and throwing his remains on the Nile.
Isis (the goddess of magic and love) did not give up and went in search of the body of her beloved husband, and she succeeded in locating it, but Seth did not stop at killing his brother, he tore his body into many pieces and scattered them around different places.
Again the loving wife did not give up, she collected the pieces after searching for them for many years and magically put them together for a certain time only, which lasted long enough to make her pregnant with their son Horus, whom Isis fought to regain the throne for and succeeded. After that she buried Osiris properly so that his soul can rest in peace.
The people of ancient Egypt celebrated Osiris's death and rebirth every year and associated it with the flood of the Nile.
Isis protected Horus during his childhood from the evil of his uncle Seth who wished to murder him, and had a long fight with him but in the end her son Horus became the Pharaoh. She was considered one of the great goddess of Egypt, and a symbol of love and magic.