Karl Wilhelm Friedrich Schlegel, German poet and critic (d. 1829)
Karl Wilhelm Friedrich (after 1814: von) Schlegel (; German: [ˈfʁiːdʁɪç ˈʃleːgl̩]; 10 March 1772 – 12 January 1829) was a German poet, literary critic, philosopher, philologist, and Indologist. With his older brother, August Wilhelm Schlegel, he was one of the main figures of Jena Romanticism.

Born into a fervently Protestant family, Schlegel rejected religion as a young man in favor of atheism and individualism. He entered university to study law but instead focused on classical literature. He began a career as a writer and lecturer, and founded journals such as Athenaeum. In 1808, Schlegel returned to Christianity as a married man with both he and his wife baptizing into the Catholic Church. This conversion ultimately led to his estrangement from family and old friends. He moved to Austria in 1809, where he became a diplomat and journalist in service of Klemens von Metternich, the Foreign Minister of the Austrian Empire. Schlegel died in 1829, at the age of 56.Schlegel was a promoter of the Romantic movement and inspired Samuel Taylor Coleridge, Adam Mickiewicz and Kazimierz Brodziński. The first to notice what became known as Grimm's law, Schlegel was a pioneer in Indo-European studies, comparative linguistics, and morphological typology, publishing in 1819 the first theory linking the Indo-Iranian and German languages under the Aryan group.