Hector Berlioz was a French composer who lived from 1803 to 1869. He is best known for his Symphonie Fantastique, which was composed in 1830 and is considered one of the most important works of the Romantic era. Berlioz was also a prolific writer, having written several books on music theory and criticism. He was an influential figure in the development of French music and is remembered as one of the greatest composers of the 19th century.