Annibale Grassi (1537–1590) was a Roman Catholic prelate who served as Apostolic Nuncio to Spain (1588–1590) and Bishop of Faenza (1575–1585).
He was summoned to Rome, where he was appointed Auditor [luogotenente] of Cardinal Guido Ascanio Sforza, who was Chamberlain [Camerlengo] of the Apostolic Camera (Finance Ministry) of the Holy Roman Church.
He was a member of the staff of Cardinal Michele Bonelli, the Pope's nephew, when he served as Legate to the Kings of Spain, Portugal, and France, in 1571 and 1572.
[2] Pope Gregory XIII, a fellow Bolognese, named Annibale a Consultor of the Holy Office of the Inquisition, and Auditor Contradictorum[3] In a letter of 24 June 1575, Pope Gregory appointed Annibale Grassi to the recently vacated post of Rector of the Studium Generale Almae Urbis (the Sapienza), an office to be held for life.
In 1576, to carry forward his predecessor's initiative, he obtained subsidies both from the city government and the Cathedral Chapter for the erection of a seminary.