Father of Mine was one of a group of four
alien villains appearing in the 2007
Doctor Who episodes "
Human Nature" and "
The Family of Blood." Initially he (and the other aliens) were clouds of green gas, and so "he" is perhaps better deemed an "it." Possessing a time-hopper, the group pursues
the Doctor in the hopes of stealing his
immortality for themselves; to avoid them, the Doctor essentially hides his Time Lord soul in a wristwatch and travels to pre-
World War I England, forgetting who he ever was and living as a
school-teacher. But a student (with a convenient brain anomaly which draws him to the watch) finds this watch and opens it, signalling the aliens to the time and place of the Doctor's hiding. It is shortly thereafter that Father of Mine takes on the human form to be associated with him in the series, possessing the stout body of neatly mustachioed Farmer Clark (played, in this human form, by Gerald Horan -- a barrel-chested actor with a career of small character roles stretching back to the mid-1980s).
One would think that, given normal roles of family authority, Father of Mine would be the leader of the group, but that role seems more to devolve upon the malevolent Son of Mine -- indeed, all of the aliens are quite cruel in their immortality quest, murdering many
innocents and creating an army of ambulatory
scarecrows to attack the Doctor's school. Naturally, the Doctor's memories are ultimately restored, and he then easily defeats the aliens. In fact, it turns out he could have done so from the start, but chose to run and hide from them in order to be merciful to them, to give them the chance to live out their mortal lives and die without feeling his vengeance. But since their avarice denied the Doctor that benediction, they are instead made to suffer for their murderous ways, in the most ironic way, for the Doctor bestows on each of them the immortality they sought, but with a terrible price -- forever trapping Mother of Mine in the event horizon of a collapsing galaxy, trapping Daughter of Mine in
every mirror in the world (where you can occasionally catch just the most fleeting glimpse of her), and freezing Son of Mine in time as a scarecrow protecting the fields of England. As for Father of Mine, his fate is actually somewhat more mundane. Encumbered with unbreakable chains forged in the heart of a
dwarf star, he is left in what seems to be some kind of underground bunker.
One must suppose, naturally, that in addition to gifting (if it can be called that) Father of Mine with immortality, the Doctor must have somehow insured that he would eternally maintain his hefty girth as well, else he might eventually simply lose enough weight to slip out of those chains. Though Son of Mine, in narrating these punishments handed out, wonders if the Doctor might ever forgive and release Daughter of Mine, the distribution of such fates in general raises the question of whether it is ever appropriate to mete out infinite consequences for finite acts, however horrific -- a common complaint about theological doctrines of eternal punishment, though more especially of concern when applied to wrongs less absolute than the murders depicted in this episode.
On a final note, the plot device of the Doctor forgetting who he is while his essence is kept in the watch is reused later in the season when it is discovered that the Doctor is not the only Time Lord remaining, another having previously done the same trick -- but this other is unfortunately the Doctor's arch-enemy Time Lord, the Master.