Leoš Janáček (3 July 1854 – 12 August 1928) was a Czech composer, music theorist, folklorist, publicist, and teacher, recognized as one of the most significant exponents of musical nationalism in the 20th century. Born in Hukvaldy, Moravia, then part of the Austrian Empire, Janáček showed early musical talent and was educated in Brno, Prague, Leipzig, and Vienna. He returned to Brno, where he married his student Zdenka Schulzová and dedicated himself to folkloristic research.

Janáček's early work was influenced by contemporaries like Antonín Dvořák. However, he later developed a unique style that incorporated Moravian and Slavic folk music, creating a modern synthesis with his studies of national folk music and transcriptions of "speech melodies." This transformation was notably marked by his opera Jenůfa, which premiered in 1904 and is often referred to as the "Moravian national opera."

Despite initial struggles for recognition, Janáček gained international acclaim with a revised edition of Jenůfa in 1916. His later works, celebrated for their originality, include operas such as Káťa Kabanová and The Cunning Little Vixen, the Sinfonietta, and the Glagolitic Mass. His compositions were influenced by Czech and Russian literature, pan-Slavist sentiments, and his infatuation with Kamila Stösslová.

Janáček's legacy was furthered by conductor Charles Mackerras, who promoted his works globally. He inspired a new generation of Czech composers, and today, Janáček is esteemed alongside Dvořák and Bedřich Smetana as one of the most important Czech composers.