When he was still able to perform, Beethoven would pointedly stop playing if he heard any of the audience members whispering. He broke a chair over the head of one of his patrons. And yet he wasn't locked up; his behaviour was taken to be evidence of his genius, and indeed his disdain for authority and social rank was so pronounced that an Archduke decreed that etiquette laws did not apply to Beethoven. He wasn't the first composer to have an Awesome Ego, just the most famous.note The first recorded case of Awesome Ego in a composer was the 15th century French composer Josquin des Prez, one of whose prospective employers was warned "he composes when he wants to, not when he is wanted" but who became so famous that dozens of works have been attributed to him that he probably didn't write; musicologists are still sorting out the mess.
The composer and impresario Anton Diabelli wrote a short waltz and asked a lot of famous composers to do a variation on it which he could then publish as a joint project in aid of orphans and widows of the Napoleonic Wars. When Beethoven finally sat down with Diabelli's tune he ran amok with it. It took him four years, but the result was the famous Diabelli Variations, the greatest set of keyboard variations since Johann Sebastian Bach's Goldberg Variations of 60 years earlier. Diabelli considered them so Badass that he released Beethoven's contribution as an independent volume, putting all fellow composers to shame. Which included big names like Franz Schubert and Franz Liszt.note To be fair, Liszt's contribution was written when he was eleven years old.
Ending Fatigue: Even some professional musicians feel that Beethoven had a hard time bringing Symphony No. 5 to an end.
Gateway Series: Both through being one of the most recognizable composers in pop culture, and having written such widely played pieces as Für Elise, the Moonlight Sonata, Ode to Joy, and the Fifth Symphony, Beethoven is many people's first introduction to Classical Music as a whole.
Growing the Beard: Some people feel that the music he wrote after he went deaf is more interesting than his earlier music.
Heartwarming Moments: At the end of the first performance of the ninth symphony, which Beethoven directed himself despite being completely deaf, the audience gave him five standing ovations - and they did it by waving hats and handkerchiefs in the air so he could see the applause he couldn't hear.
Narm: "Wellington's Victory" commemorates the Battle of Vitoria by playing the opposing countries' national anthems ("Rule Britannia" and "God Save the King" for the British, and "Marlbrough s'en va-t-en guerre" for the French) and a battery of artillery percussion effects. It's exactly as corny as it sounds, but it was a big hit in its day which helped pay the bills. Beethoven apparently had no illusions about its musical quality, but defended himself from critics by remarking, "What I shit is better than anything you could ever think up!"
Sampled Up: Henry van Dyke's hymn "Joyful Joyful We Adore Thee" is set to Ode to Joy.
Vindicated by History: The premiere of the Fifth Symphony (and the Sixth) was in a concert that lasted four hours on a cold, December night and the audience was tired. Needless to say, it was not very well accepted in its first performance. It took a review by E. T. A. Hoffmann to bring its genius to light. However, It Makes Sense in Context - the premiere was during the Napoleonic Wars, and as a result the orchestra was only able to rehearse the piece once before the performance, and mangled it so badly that Beethoven was forced to stop and restart at one point.