A Great President of the Goetia commanding thirty legions, whose historical entry is brief and oddly gentle: he appears as 'a poor child with angel's wings, riding on a two-headed dragon,' and his offices are to give true answers of hidden treasures and to reveal where serpents may be seen, delivering them harmless to the operator.
That is the entire pre-modern record: a treasure-finder and snake-handler in the shape of a winged boy. There is no nun. The archive states this plainly because The Conjuring 2 (2016) introduced 'Valak, the Defiler, the Profane, the Marquis of Snakes' as a demonic nun, and the image has since bled backward into popular accounts of the historical spirit — a live case study in how fiction contaminates folklore in real time, of a piece with The Exorcist's remodeling of Pazuzu.
The snake association is the single genuine thread between the two. Everything else on the modern file arrived by screenwriter.