Explain how the deity horus became the king of egypt and osiris became king of the underworld

Osiris was the king of Egypt before.
Horus had a evil brother named Set
who was jealous of Horus He killed him and became King of Egypt. 
Later Osiris's wife Isis collected his body and breathed life into it.
They had a child named Horus the hawk god who avenged his father and killed Set.Horus then claimed himself as king of Egypt.   

This image can be found in the Amiens Cathedral.