According to The Monk Zone:
With the arrival Thelonious Sphere Monk, modern music — let alone modern culture — simply hasn’t been the same. Recognized as one of the most inventive pianists of any musical genre, Monk achieved a startlingly original sound that even his most devoted followers have been unable to successfully imitate. His musical vision was both ahead of its time and deeply rooted in tradition, spanning the entire history of the music from the “stride” masters of James P. Johnson and Willie “the Lion” Smith to the tonal freedom and kinetics of the “avant garde.” And he shares with Edward “Duke” Ellington the distinction of being one of the century’s greatest American composers. At the same time, his commitment to originality in all aspects of life — in fashion, in his creative use of language and economy of words, in his biting humor, even in the way he danced away from the piano — has led fans and detractors alike to call him “eccentric,” “mad” or even “taciturn.” Consequently, Monk has become perhaps the most talked about and least understood artist in the history of jazz.The WikiWackyWoo says, "Monk is the second-most recorded jazz composer after Duke Ellington, which is particularly remarkable as Ellington composed over 1,000 songs while Monk wrote about 70."
It wasn't just his own compositions. When Monk covered another artists' song, he had a way of turning it inside out and creating his lovely dissonance, where it none had before.
Clint Eastwood, when he's not berating empty chairs, is a great aficionado of Jazz. He produced this 1988 documentary, directed by Charlotte Zwerin that can say far more than I can:
If that has whetted your appetite, here's a Thelonious Monk Jukebox I put together: