Merlin's father

The father of Merlin and his younger half-sister Ganeida was a mysterious individual.

He was said to be a demon; although Agamya Akhtar suggested this may simply have been Camelot's way of stating that he was an alien of some kind, his hybrid children did derive actual magical abilities from their half-human parentage, both becoming wizards. According to Merlin, he did not realise, following his brief fling with Ganeida's mother, a nun, that he had produced a second offspring; he only remembered to check several decades after her birth. Merlin noted that it was "just like him to forget about someone for a few decades". (PROSE: A Honeycomb of Souls)

Behind the scenes
If the "half-demon" Merlin seen in A Honeycomb of Souls is the same as the version of Merlin documented in Battlefield and connected media, this would make his and Ganeida's father the Time Lord Ulysses.

Although Merlin's demonic parentage is documented in many medieval and later sources, starting with Geoffrey de Monmouth's version of the Arthurian legends, his demon father is not usually named. Some versions claim that Merlin was an attempt to birth the Antichrist, however, which would identify his father as no ordinary demon but as the Devil himself.