On the series finale when Mulder is being held and questioned they ask him "what are you thinking abouot?" He replies "My son, his mother". From that I think we can safely asume it was Mulder´s son.
posted over a year ago
He also could use this phrase because he feel like William's stepfather ;) Who is William's father - it was, it is and it will be a mistery - the last great mistery of X-Files :)
Yeah they never say excatly but its most likely mulder because scull names her baby "william" after mulders father.
posted over a year ago
It could also be after her own father, I know she tells Mulder it was after HIS father but I always kinda thougth it was for both of them. Besides, Mulder's father was kinda evil...
Mulder is the father. Even though it's never confirmed, Scully and Mulder refer to him as "our" son. They reveal that the government tampered with the mothers egg, but they'd still need someone (a man) to conceive the child.