Cosimo Fanzago (Clusone, 12 October 1591 – Napoli, 13 February 1678) was an Italian architect and sculptor, generally considered the greatest such artist of the Baroque period in Naples, Italy.
Fanzago was born in Clusone (current Province of Bergamo) in a family of bronze-casters and architects. In 1608, after a short stay in Chieti, he moved to Naples. Here (according to what he wrote in 1612) he trained as a marble sculptor (maestro di scultura di marmo) and mason under the Tuscan sculptor Angelo Landi. His first important work was the sepulchre monument of Mario Carafa, a relative of Cardinal Carafa. His architectural debut was the design of San Giuseppe dei Vecchi a San Potito (completed 1669).
According to an essay about Fanzago's life by count Fogaccia, in Naples he obtained the support of the Benedictines, the Viceroy Duke of Medina, Prince Caracciolo and the Carthusians, and soon opened a workshop of his own.
Apparently he sympathised with Masaniello's revolt, and after the return of Royal authority, Fanzago was sentenced to death and had to flee to Rome, where he worked for a decade. He returned to Naples and designed the initial layout church of Santa Maria Egiziaca a Pizzofalcone (built 1651–1717). This church displays a Greek cross plan, and resembles a hybrid of contemporary Baroque masterpieces by Bernini (dome resembles Sant'Andrea al Quirinale) and Borromini (the plan resembles Sant'Agnese).