You've never heard of him because he was a playwright, not a composer. However, both Rossini and Mozart (!) took his plays and made them into sublime operas. They loom so large in the Canon that no less than Bugs Bunny performed each of these.
Highbrow entertainment for the rugrats, indeed.
The story of these is much more interesting than you might think. The French polymath Pierre-Augustin Caron de Beaumarchais wrote a series of subversive plays in the 1780s. Beaumarchais was a genius, who had come to the attention of the French court of Louis XV by creating a much more accurate pocket chronometer - actually one that was small enough to be mounted on a finger ring. But Beaumarchais was more than a bit radical, an early supporter of the American Revolution against the British Crown and a popularizer of the idea of the Rights Of Man.
His plays featured the hero Figaro, the smarter servant of a dim nobleman - essentially an Eighteenth Century Jeeves and Wooster, set in Ancien Régime France. Unfortunately for him, he needed the approval of the French Crown censors to publish. Even a fellow like Beaumarchais (who had the King himself wearing his chronometer ring) had to work for years to get published. The Barber was performed in 1775. The sequel, the Marriage of Figaro was stalled until its first performance in 1781 but then was immediately banned again by the new King, Louis XVI.
The King was particularly unhappy at how the nobility was mocked. Beaumarchais was relentless, however, and kept giving private reading of the play, building support until the King finally relented and let it be performed in 1784. Two years later Mozart himself wrote an opera based on Beaumarchais' play. It caused a scandal when it was premiered in Vienna, but the music is sublime (if subversive to Eighteenth Century nobility).
If you wish to dance, my dear Count
it is I who will call the tune
In 1816, Rossini enshrined this subversive story in history is his epic Il barbiere di Siviglia. By then the Ancien Régime was long gone and Napoleon had come and gone. Mozart was dead, and the day had passed to Beethoven and the Romantic Movement. All that remained was inspired cartoonists at Warner Brothers who in a brief flash of inspiration did not underestimate their audience.
In a way, the Warner Brothers cartoonists were cut from the same bolt as Beaumarchais himself. Beaumarchais refused to underestimate or condescend to his audience, and so his plays were banned for being seen - accurately, one must admit - as entirely subversive to the order of the day. Warner Brothers was similarly subversive, refusing to condescend to its adolescent audience. In every way imaginable, this is the height of American popular television.
Bootnote: Warner Brothers Bugs Bunny episode was an instant classic, to the point that other cartoons did their own version, Here's Woody Woodpecker: