Giuseppe Piazzi was an Italian Catholic priest of the Theatine order, mathematician, and astronomer. He established an observatory at Palermo, now the Osservatorio Astronomico di Palermo – Giuseppe S. Vaiana. He is perhaps most famous for his discovery of the first dwarf planet, Ceres.

The Theatines, officially named the Congregation of Clerics Regular, is a Catholic order of clerics regular of pontifical right for men founded by Archbishop Gian Pietro Carafa on 14 September 1524.