House of Farnese
Ranuccio belonged to the House of Farnese, whose duchy were founded by his patrilineal ancestor, Pope Paul III, formerly Alessandro Farnese. The Farnese Dukes had been ruling Parma and Piacenza since Pope Paul's illegitimate son Pier Luigi Farnese was given it as a possession. Pier Luigi was also Duke of Castro, a title he was bestowed upon by his father, after the latter created it from the lands recovered after the death of Ranuccio the Elder, Pier Luigi's younger brother.