What was the first composer and how was his style?

Answer 1

The first composer in the Western musical tradition who is at all famous is actually a she - Hildegard of Bingen, born in 1098, at the time of the First Crusade. She was a polymath whose compositions were popularised within the Early Music community by the award-winning CD A Feather on the Breath of God: Sequences and Hymns by Abbess Hildegard of Bingen. In 1151 she wrote what is widely regarded as the first morality play, Ordo Virtutum("Order of the Virtues").

The first composer in the traditional Western canon is the Frenchman Magister Leonin (before 1150-1201), who wrote some of the first polyphonic music (i.e. music consisting of two or more voices moving independently), a principle that underlies nearly all subsequent Western music. He was probably also one of the first to use and to devise a notation for the rhythmic modes. These were a way of regularising what had been the rhythmically indeterminate "free" rhythm of plainchant, at least in the way it was notated (see also below).

You should note that there were doubtless composers long before this - among others, those who wrote the various plainchants (often called "Gregorian" chants") that still survive. Most of these were anonymous, however.