From Discworld & Terry Pratchett Wiki
|Occupation||High Priest of Blind Io|
|Parents||Mother is presumably still alive and living on the family estates.|
|Relatives||brother Mustrum Ridcully|
|Marital Status||married - the name of Mrs Ridcully is unknown.|
|Cameos||Reaper Man, Feet of Clay, The Truth, The Last Hero|
Ankh-Morpork could hardly have a state religion. Which of the two or three thousand significant gods would it follow, and what about the possible offense to the others? No, separation of Church and State is a no-brainer, lest the State be separated from the firmament. Still, there are occasions when a nod must be directed toward Dunmanifestin, or consultation seems in order over the religious implications of some policy. At these times, the practical choice of a spiritual leader and spokesman is the High Priest of Blind Io, the Chief of the gods. Io does not actually have the most followers, but his religion doesn't demand much from them, or cause much political disturbance; it's safe and bland.
So is the High Priest, Hughnon Ridcully, a bureaucrat in priestly vestments. Ridcully is an organizer, an executive. His co-religionists tend not to burn with any great evangelical fervor, and Hughnon's flame is as low as any. His job is to see that the temple's bills are paid and windows cleaned. He can deliver a sermon of the usual platitudes whenever required, but he won't spend any time actually fussing about the flock's immortal souls. His religion serves to provide him with a comfortable and prestigious job. Another selling point for Hughnon as the official voice of religion is that his brother, Mustrum, is the Archchancellor of Unseen University and therefore the most powerful wizard around. In addition, it appears that Blind Io grants him a bit of divine power or protection from harm, at least when he bothers to pay attention; lightning hurled by the other gods fails to hit Hughnon (see Feet of Clay). As such, he maintains his power over the other religions of Ankh-Morpork quite easily.
Although without the authority of "State Religion", Hughnon Ridcully fills, approximately, the position occupied in another post-imperial society by the Archbishop of Canterbury. In Hughnon's case, he presumably attained his position when his predecessor was burned to ashes in Guards! Guards!.
We learn in The Last Hero from an aside to one his underlings that, unlike his brother Mustrum, Hughnon is married. (Faced with a long emergency debate in Synod, he sends a lowly deacon off to inform his wife that he may not be home tonight, and could she please have the kindness to pack him an overnight bag). So evidently priests, unlike wizards, may marry. The name, and indeed further details, concerning Mrs Ridcully are unknown, nor is it known if there are any children. However, we know enough about the Ridcully family to know that they are well-to-do country landowners with wide estates - indeed, Mustrum retired from active Wizarding for a long time in order to manage the family estates. (This implies that there are no other siblings and that Father may not be alive). It is also known from an exchange between the brothers in Reaper Man that Mother is still alive, and vexed that she doesn't get letters from Mustrum as often as she could.
Therefore as typical representatives of the upper classes, one of the Ridcully brothers must have been taxed with producing heirs who may inherit the family wealth. So it is more than likely that there are younger Ridcullies: children of Hughnon and nephews/nieces to Mustrum. This is a most interesting prospect!
And at least in the British upper classes, there is still an axiom that where there is more than one son, the eldest (heir) inherits: the younger (the spare) are packed off into the professions, ie the military, the law, academia, and (for perceived idiot sons who are otherwise unemployable) banking. Or the Church...