Pierre Beaumarchais
In 1786, Wolfgang Amadeus Mozart composed an opera, "Le Nozze di Figaro", based on "The Marriage of Figaro", with a libretto by Lorenzo Da Ponte based on the play. Several composers including Paisiello in 1782 wrote operas based on "The Barber of Seville". Rossini's 1816 version is his most successful work and still often performed. In 1966, Darius Milhaud composed an opera, "La mère coupable", based on "The Guilty Mother".
Nicolas-François Guillard
Nicolas-François Guillard (16 January 1752 – 26 December 1814) was a French librettist. He was born in Chartres and died in Paris, the recipient of a government pension in recognition of his work writing librettos. He was also on "Comité de Lecture" of the Paris Opéra. One of the foremost of the French librettist of his generation, he wrote libretti for many noted composers of the day, including Salieri ("Les Horaces") and in particular Sacchini ("Œdipe à Colone", amongst many others). His most famous work is "Iphigénie en Tauride", his first libretto, set by Gluck after the composer had initially rejected it. Gluck collaborated with Guillard to heavily recast the libretto, not only to suit Gluck's artistic preferences, but also to accommodate pre-existing music that Gluck borrowed, both from himself and from other composers, when composing the opera.