Britten (1913-1976) was a British composer, who is generally regarded as a very important figure in 20th century classical music. In spite of that, it is remarkable that many people know very few of his works. Personally, I think his operas are the best since Richard Strauss, and the War Requiem for soprano, tenor, baritone, boys' voices, chorus, chamber orchestra, orchestra and organ, Op. 66, from 1961 is simply sublime. Relevant links below.