Olivier Eugène Prosper Charles Messiaen (UK: , US: , French: [ɔlivje mɛsjɑ̃]; 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; harmonically and melodically he employs a system he called modes of limited transposition, which he abstracted from the systems of material generated by his early compositions and improvisations.
Béla Viktor János Bartók (; Hungarian: Bartók Béla, pronounced [ˈbɒrtoːk ˈbeːlɒ]; 25 March 1881 – 26 September 1945) was a Hungarian composer, pianist, and ethnomusicologist. He is considered one of the most important composers of the 20th century; he and Franz Liszt are regarded as Hungary's greatest composers. Through his collection and analytical study of folk music, he was one of the founders of comparative musicology, which later became ethnomusicology.