The House was founded by Giacomo Attendolo, a condottiero from Romagna who would pass his nickname of Sforza to his descendants. His son Francesco would become Duke of Milani in 1450, after the extinction of the Visconti line.
Francesco's successor was his son Galeazzo Maria, who was assassinated in a Templar plot orchestrated by Rodrigo Borgia on 26 December 1476 despite the Assassin Giovanni Auditore's best efforts to save the Duke. Galeazzo's brother, Ascanio, had instead pursued an ecclesiastical career and later became cardinal.
While Galeazzo was succeeded in Milan by his brother Ludovico, he had also sired an illegitimate daughter, Caterina, who would later become Countess of Forlì and Imola, and an important ally to Ezio Auditore da Firenze.
A cadet branch of the family, descending from Muzio's second son Alessandro, had also been ruling Pesaro and Gradara. Alessandro's grandson Giovanni Sforza was the first husband of Lucrezia Borgia, before their marriage was annulled by the Pope, much to Giovanni's scorn.