Composer and musician Ludwig van Beethoven was only 26 years old when he began to lose his hearing. By this time he had already established himself as a fine pianist and teacher, but he had only published a few piano sonatas. His first symphony would not be published and performed until 1801. Thus his early-onset deafness affected almost the entire span of his musical career.
His symptoms began as a minor annoyance but developed into full-blown tinnitus, a ringing noise medically defined as "the perception of sound within the human ear in the absence of corresponding external sound" (Wikipedia). Historians and doctors have since debated the cause of his tinnitus, which could have originated with syphilis, typhus, lupus, or even lead poisoning.
Beethoven admitted to his growing deafness as early as 1801, when he described the difficulties he had in appreciating music and following conversations. After retreating to Austria in an to attempt to come to terms with his condition, he wrote to his brothers--the famous Heiligenstadt Testament, in which he vowed to live life through his art. This initiated his prolific and profound "Middle Period" of composition, but marked a significant decline in his ability to perform in public.
Because public performances and piano competition had been a lucrative part of his income--a financial mainstay of his contemporaries--he suffered lapses into poverty when between patrons. Frustration and embarrassment may have contributed to his reputation for being grumpy, loud, unmanned, and generally unpleasant. His close friends knew the cause, but few others did.
After a disastrous interpretation of his 5th Symphony in 1811, Beethoven never played in public again. He was completely deaf by 1814. Quite famously, he could not hear the overwhelming applause when his masterful 9th Symphony was debuted in 1824. Here the scene is portrayed in Immortal Beloved:
Although Beethoven left us with a staggering catalog of some of the best music ever composed, he was unable to appreciate his creations as we do. He heard his music only in his mind. To communicate with people, he used notebooks that continue to offer musical scholars priceless insight into his opinions and thought processes. But Anton Schindler, an associate and early biographer of Beethoven, burned 264 of the 400 notebooks in an attempt to clean up the composer's image and maintain a sense of aura around his process--so not even that aspect of Beethoven's tale escaped a tragic ending.