Rider's identity is Ramesses II, the third pharaoh of the Nineteenth Dynasty of Egypt. He likes to refer to himself as the King of Kings, and also prefers being addressed as Ozymandias by other Servants and people.

He was friends with Moses in his life, and holds a special place in his heart for one of his wives, Nefertari. However, it could be that their friendship ended when Moses became the prophet of the Israelites and began to preach the teachings of God, denouncing the gods of Egypt.

(Source: Type-Moon Wiki)