There are many great composers, both well-known and obscure, living and deceased. I'm thinking now of one who wrote two of those snippets that kids who don't know how to play the piano teach each other - the first four notes of probably the most famous symphony ever written, and a piano piece best known by its opening nine notes. This seems appropriate, because he was also the hero of the musical Peanuts character Schroder.
The famous tune at the end of his greatest and last symphony influenced the main tune Brahms placed in the last movement of his own first symphony, and Brahms put off writing symphonies until he was in his forties because of the impact of this musical giant. When the similarity was pointed out to Brahms, he famously said, "Well, any ass can see that!" (To our moderator and offended readers: he intended the older meaning of the word.) Who prompted Brahm's defensive remark? I bet you've guessed long before now. As the man said of himself, "There is only one Beethoven!"
I'll never forget the first time a piano teacher assigned me a "real" piano sonata of his, a short early one in G minor which ended up being published later in his life. Just seeing his name in the upper right hand corner of the page made me feel like I was leaving kiddie pieces behind and entering the piano world of grown-ups. Of all the composers I had encountered to that point, his name filled me with the greatest reverence.
Beethoven has been a constant figure in my life, and unfortunately, I've sometimes taken him for granted. Since his music is much more familiar to me now, I've followed many interests, getting to know other musical masters, and becoming interested in the music of others who've been virtually forgotten. I can't stay away from Beethoven for too long, however.
When I think about it, I still marvel at the sheer effort that writing music required of him, both physically and emotionally. He was famously temperamental, obsessed with music to the exclusion of other things and people in the world. He worked with sketchbooks, in which he re-wrote some themes over and over, hammering away at them 'till he got them right. Even his manuscripts are not always clean and pretty, like those of other famous composers; they contain sections which are crossed out and torn, and they can be very messy. Here's one example from his sixth symphony (http://www.bl.uk/onlinegallery/themes/music/beethoven.html). Here are parts of the 9th Symphony (http://beethoven.staatsbibliothek-berlin.de/de/sinfonien/9/1/1.html), in which some sections are messier than others.
It's also amazing to me that whole groups of pieces he composed in a particular genre, say piano sonatas or symphonies or string quartets, are not only strings of masterpieces - not a dud to be found anywhere among them - but they have had perhaps the greatest influence over those symphonies or sonatas or quartets which came after them. I think lots of musicians and music lovers would agree with that. Beethoven's influence is also tied to something else about him that really keeps us hooked: his personality itself seems to have survived more fully somehow, inside his notes and words, and it still compels us. When you get to know the drama of his life, it's easier to understand his tirades and have sympathy for his sufferings, both of which can also be heard in his music.
If you'd like to spend time with Beethoven, we've got some great books, recordings, and films to offer. I recently watched "Copying Beethoven" (whose release slipped by me in the theater). This film focuses on the last years of Beethoven's life, and while it fictionalizes many details, I enjoyed Ed Harris's rather vigorous portrayal of the composer and his struggle to complete and perform his 9th Symphony. (More than 20 years after I first encountered the whole piece, this remains my favorite symphony.) Compare this with Gary Oldman's portrayal in Immortal Beloved, which takes its title and plot focus from some of Beethoven's letters (http://www.usnews.com/usnews/doubleissue/mysteries/immortal.htm). Both films are more succesful as entertainment than as biography (as their creators intended, I think); if you want to get a sense of the "real" Beethoven, try one of the biographies by Lewis Lockwood or Maynard Solomon.
I'd like to close with these few words from the great man himself, "I wish you music to help with the burdens of life, and to help you release your happiness to others."