Roland Deschain impregnates an oracle and sires a child named Mordred. Mordred is the canonical answer in Stephen King's The Dark Tower series.
The conception is deliberately supernatural and grotesque. The oracle is a demon elemental, and Roland's semen is later altered with the Crimson King's influence before being used to impregnate Susannah Dean. The pregnancy is carried by Mia, another supernatural being who inhabits Susannah's body.
Mordred is therefore described as having two fathers—Roland and the Crimson King—and two mothers, Susannah and Mia. He is a half-human, half-spider creature with the ability to change form, reflecting the series' Arthurian mythology and its recurring themes of doubles, cycles, and corrupted destiny.
A common mix-up is to treat Mordred as simply Roland's biological son or as the Crimson King's ordinary offspring. The books present him as a uniquely shared, prophetic child. He is born in The Dark Tower and later becomes a threat to both Roland and the Crimson King before his own fatal weaknesses bring about his downfall.