The Master of Yimsha was once human a long time ago. Nobody knows when and where he was born, but one thing is certain: he has ceased to be a human being since he gave his soul to the forces of evil. He is the Master of all the Black Seers and possesses untold evil powers and can manipulate minds and reality as he pleases.

"Not I!" he laughed. "I was born on this planet, long ago. Once I was a common man, nor have I lost all human attributes in the numberless eons of my adeptship. A human steeped in the dark arts is greater than a devil. I am of human origin, but I rule demons. You have seen the Lords of the Black Circle—it would blast your soul to hear from what far realm I summoned them and from what doom I guard them with ensorcelled crystal and golden serpents.

Robert E. Howard - The People of the Black Circle

Map of the Hyborian age :