Olivier Messiaen (French pronunciation: ; December 10, 1908 – April 27, 1992) was a French composer, organist and ornithologist, one of the major composers of the 20th century. His music is rhythmically complex (he was interested in rhythms from ancient Greek and from Hindu sources); harmonically and melodically it is based on modes of limited transposition, which he abstracted from his early compositions and improvisations. Many of his compositions depict what he termed "the marvellous aspects of the faith", and drew on his deeply held Roman Catholicism.