I'm going to do one more of these today, because it's short. Meet the composers brought to you by the letter I...
Ibert (Jacques) wrote operas (some of them in collaboration with Honegger), symphonic poems, piano music, film scores, and incidental music for the theatre. This composer on the "lighter side" of fine-art music is mainly remembered, I think, for his concertos for flute and saxophone.
Ippolitov-Ivanov (Mikhail) is an extremely minor Russian-Soviet composer, a pupil of Rimsky-Korsakov and a teacher of Glière. His only works still widely performed are excerpts from his suite Caucasian Sketches (the title refers to a region, not a race) and his completion of Mussorgsky's unfinished opera The Marriage.
Ireland (John), an Englishman, is considered an "impressionist" composer in the tradition of Debussy and Ravel. He wrote a good deal of songs and sacred music, including a setting of the Communion Service and a beloved tune for the hymn "My song is love unknown." He is chiefly remembered for a song called The Holy Boy, which he also arranged for cello & piano, organ, and string orchestra; and for A Dowland Suite, completed after his death.
Isaac (Heinrich) was a 15th- and 16th-century composer, an inferior conterporary of Josquin, best known for his beautiful madrigal Innsbruck, ich muss dich lassen. Later adapted into the hymn tune O Welt, ich muss dich lassen (O world, I now must leave thee), it has been used in Lutheran hymnals and the chorale-based works of such composers as Bach, Brahms, and Reger. He also published an enormous collection of liturgical motets called Choralis Constantinus.
Ives (Charles) made a fortune in the insurance business, which he used to bankroll his own career as a composer (more of a hobby, really). Later, after he mysteriously stopped composing around 1927, he bankrolled the music of other progressive and experimental composers instead. Ives wrote numerous songs, plus such orchestral novelties as The Unanswered Question, Central Park in the Dark, two "orchestral sets" (including Three Places in New England), and four completed symphonies. These are very controversial works - marked by a spirit of curiosity, adventure, and self-taught genius, but also highly dissonant, uncompromisingly erudite, and difficult to perform. One of my favorite music-related quotes comes from Ives: "Sit down and take a good dissonance like a man!"