Nicolò Francesco Leonardo Grimaldi (5 April 1673 (bap) – 1 January 1732) was an Italian mezzo-soprano castrato who is best remembered today for his association with the composer George Frideric Handel, in two of whose early operas he sang.
Between 1697 and 1731 he sang many operatic roles at various Italian cities in works by composers such as Alessandro Scarlatti, Nicola Porpora, Leonardo Vinci, and Johann Adolph Hasse.
Other composers who wrote major roles for him included Francesco Provenzale (who was his teacher), Pollarolo, Ariosti, Lotti, Giovanni and Antonio Maria Bononcini, Caldara, Albinoni, Leo, and Riccardo Broschi.
The eighteenth-century musicologist Charles Burney described Nicolini as "this great singer, and still greater actor", while Joseph Addison labelled him "the greatest performer in dramatic Music that is now living or that perhaps ever appeared on a stage".
In 1731 he planned to sing at Naples in Giovanni Battista Pergolesi's first opera seria, La Salustia, but became ill and died during rehearsals.