Mendelssohn

Born into a wealthy Berlin banking family; his grandfather was the philosopher Moses Mendelssohn. He wrote the Midsummer Night's Dream overture at seventeen, and that weightless flickering string writing became his signature. In 1829, aged twenty, he conducted the first performance of the St Matthew Passion since Bach's death and more or less single-handedly returned Bach to the repertoire.

His music almost never tears, which later Romantic critics held against him — Wagner's notorious essay on the subject is the ugliest example. But the Violin Concerto remains the most-played concerto for the instrument: the soloist enters immediately, giving the orchestra no chance to set the scene, and the three movements run without a break. That is a genuine formal innovation, not a pleasantry.