In Egyptian mythology, Ra-Horakhty was more of a title, or manifestation, than a composite god. It translates as "Ra (who is) Horus of the Horizons". It was intended to link Horakhty (as a sunrise-orientated aspect of Horus) to Ra. It has been suggested that Ra-Horakhty simply refers to the sun's journey from horizon to horizon as Ra, or that it means to show Ra as a symbolic god of hope and rebirth. This link was probably encouraged by Ra and Horus' common link to the sun and the Pharaoh.
This monster's attack name is Djeser, which means holy in ancient Egyptian language. The Mortuary Temple of Queen Hatshepsut is named Djeser-Djeseru that means Holy of Holies.
It is likely that Obelisk the Tormentor, Slifer the Sky Dragon and Winged Dragon of Ra are manifestations of Horakhty, given that they fused to form it.