Daimon Hellstrom was born to a mortal woman, but his father was Satan!* Y'see, Satan had concocted a ridiculously-elaborate plan that involved coming to Earth, seducing and marrying a mortal woman, and then having two kids, Daimon and his sister Satana. Eventually, Satan's true identity was revealed, the woman went insane, and the family was split up. Daimon was raised normally in an orphanage, and only learned of his demonic heritage from his mother's diary when she died.
With tremendous magical powers at his command due to his birthright, Daimon would fight his demonic heritage by becoming a demonologist and exorcist under the name of the Son of Satan. He fought against his father and sister at different points, along with various demons and occult menaces.
*Not the real Satan, but a lying yet powerful demon