Nepotism
For instance, Pope Callixtus III, head of the Borgia family, made two of his nephews cardinals; one of them, Rodrigo, later used his position as a cardinal as a stepping stone to the papacy, becoming Pope Alexander VI. Alexander then elevated Alessandro Farnese, his mistress's brother, to cardinal; Farnese would later go on to become Pope Paul III. Paul III was a notorious nepotist. When elected Pope in 1534 he appointed two nephews, aged 14 and 16, as cardinals.