Oh, Brahms. In 1890, at 57, having grown his famous beard, he thought he'd retire from composing, not in any despairing way, but just feeling he'd said what he needed and wanted more time doing nothing—he was dating, in fact, for the first time since his broken engagement of 1859, a 28-year-old mezzo-soprano, Alice Barbi, whatever that may have meant in Vienna in 1890, and hanging out with the most famous pop musician in Vienna at the time, Johann Strauss II, who was eight years older than he was. But when he went to a music festival in Meiningen in January 1891 and heard the clarinetist Richard Mühlfeld playing the Weber concerto and the Mozart clarinet quintet, the dark intimacy of the instrument's sound with a genius player gave him a longing to do that thing, and he unretired himself, writing a trio, a quintet like Mozart's which is the one I love best, and two extraordinary sonatas, of which this is the second. Among a bunch of great pieces that are not for clarinet.
OK here's the trio too.