The Colleoni were a Guelf-allied family in medieval Bergamo. Their Ghibelline opponents were the Suardi.
When the Visconti of Milan seized Bergamo, they exiled the Colleoni and other Guelfs. On October 23, 1404, Paolo Colleoni seized Trezzo Castle by wile and held it by force until he was assassinated by his cousins, probably acting on behalf of the Duke of Milan. Paolo's son Bartolomeo became a famous mercenary and Captain-General of the Republic of Venice. He purchased and refurbished the Malpaga Castle in Cavernago as a new base for his family. The Colleoni Chapel in Bergamo was built in his honor and houses his remains and those of his beloved daughter Medea.
Bartolomeo's grandson Count Alessandro Martinengo Colleoni commissioned Lorenzo Lotto's 1516 Martinengo Altarpiece for the Dominican church of Santi Bartolomei e Stefano in Bergamo.