Prince Ra-Man was a young prince from the Ra-Realm who died accidentally 4,000 years ago. He was reputed to be a descendant of the Egyptian sun-god, Ra.
However, he was later reborn when supernatural sleuth, Mark Merlin escaped one of his old enemy's by shrinking himself, and then vanishing into the dimensional Ra-Realm. There, Merlin met the Egyptian scientist, Kranak and his daughter Rimah.
When Merlin wanted to return to Earth, Kranak told him he couldn't, at least not as Mark Merlin. His body and soul would have to remain in the realm of Ra, otherwise he would die. Kranak suggested that Merlin's memories could be reincarnated as "Prince Ra-Man." Agreeing to this, Merlin absorbed the rays of a potion provided by Kranak and he successfully returned to Earth transformed as the Egyptian prince, yet maintaining Merlin's memories and black magic abilities.
Once Prince Ra-Man arrived at Merlin's Mystery Hill Mansion, he took the detective's place as a sorcerer. He explained to Elsa, Merlin's assistant, his transformation by telling her that Mark Merlin was now dead, and that he was his friend, contacted by occult means to come and save her.
Prince Ra-Man had a very short career as a supernatural hero. He fought Eclipso on a few occasions, but ultimately he sacrificed his life in battle against the Anti-Monitor's Shadow Creatures during the Crisis.
Following the Prince's apparent death, Mark Merlin has apparently returned to life. He was seen in Gotham City, helping the Penguin by communicating with the dead.
More recently, when the Parasite was draining the magical abilities of Zatara, It was Merlin who rescued him and then tried to recruit the magician for a mission to find the missing Prince Ra-Man.
It should also be noted, that when Zatanna went looking for her father’s books of knowledge, her trans-dimensional journey into magical realms gave her a chance to meet the newly dubbed "King Ra-Man," who stated that he was the creator and watcher of Ra-Realm.