Prester John

Prester John was a myth that turned out to be a fairytale.
Christian European nations since the early middle ages attacked and were attacked by their Islamic counterparts such as the Ottoman Turks. So how does Prester John play into this? It was believed that he was the ruler of a powerful kingdom located in the midst of Islamic kingdoms making him a formidable ally since Prester John, as legend had it, was a Christian.
Well the Europeans, specially the Portuguese and the Spanish, looked for this guy as they made their way into Africa from the late fourteen hundereds on.
They never found him since he never existed.