Djedefre became pharaoh after his father Khufu died. Unlike his dad, his brother Khafre, and his nephew Menkaure, Djedefre didn't build a pyramid at Giza; he chose to build at a site called Abu Roash instead. No wonder you probably never heard of him!
Djedefre was the first pharaoh to add the title "Son of Re" to his birth name.
Ruins of Djedefre's Pyramid. By No machine-readable author provided. AhlyMan assumed (based on copyright claims). [Public domain], via Wikimedia Commons
Red granite head of Djedefre. By Louvre_032007_19.jpg: Neithsabes derivative work: JMCC1 (Louvre_032007_19.jpg) [Public domain], via Wikimedia Commons
= "son of Re"
Watch: "The Lost Pyramid of Djedefre"