Jean Sibelius (1865–1957) is the most well-known of Finnish classical composers. Today is a public flag day in Finland (Jean Sibeliuksen päivä), commemorating Sibelius and Finnish music.
Finlandia (and especially the Finlandia Hymn part) is perhaps the most famous of his compositions. The Liverpool Philharmonic’s version is lovely:
Jean Sibelius, Finlandia performed by Royal Liverpool Philharmonic Orchestra and Vasily Petrenko by Liverpool Philharmonic
Here’s a version of the Finlandia Hymn by Cantus Vocal Emsemble, with lyrics (I believe) from a Unitarian Universalist hymn book:
The Finlandia Hymn by cantussings
While Finlandia and the Finlandia Hymn are incredibly popular, they are by no means alone. I’m very fond of this intermezzo from his Karelia suite, for example:
Jean Sibelius: Karelia – Intermezzo I from legrandchene
I’ve been playing my Sibelius all morning while working. Hyvää Jean Sibeliuksen päivää!