The downfall of the 4th dynasty and the start of the 5th dynasty is one of the most complicated historical problem of the Old Kingdom. Queen Khentkaus I - a daughter of the Pharaoh Menkaure played a significant role at that time. When the mail royal stem died off in male tail, she was the one who became a royal mother and a connecting link between the 4th dynasty and solar kings. Rulers of the 5th dynasty are sometimes called with this name.
Her son Userkaf was the first Pharaoh of the 5th dynasty. He usurped the throne of the king Shepseskaf. The title "son of Ra" was on its top under his rule, this title became a part and parcel of king's titling.
Userkaf founded the first sun temple right in Memphis' necropolis. Its name was Nekhen of Ra and it was placed at recent village Abusir on a pretty distant place then. It is one of two discovered sun temples.