My favorite composer of all time is Béla Bartók.
Because his music is bold, vital, and brilliant. His rhythms get my blood flowing. His melodies sometimes ache with sadness, other times they're giving the finger to the world. He was not afraid of the weird or the dark side (Miraculous Mandarin). His piano book Mikrokosmos unleashed my abilities to play and invent new music on the piano, beginning with quartal chords and asymmetric Balkan folk rhythms. His six String Quartets are universally considered the ultimate in string quartets since those of Beethoven.
Bartók listened to the common people, recorded their old-time music before it disappeared, presented it to the world, and created an innovative new way of composing based on it. In 1905 he was traveling on ox-carts over rutted dirt roads into remote villages, using a hand-cranked wax cylinder phonograph to record folk music whose living memory extended back to the early 19th century, but most of which was much older. Traveling around like that was hard work, but his efforts yielded the richest archive of really old folk music ever recorded. To give this some perspective: Bartók included notes to his modernist setting of "New Hungarian Folksong" explaining that "new" means mid-19th century. The old ones are centuries old. He traveled to many nations and recorded their peasants' old music like this. By doing so he uncovered varieties of harmony, rhythms, and scales that allowed a radical departure from conventional classical music while still being rooted in the grassroots of the people. A feeling organically connected to music tradition, yet innovative. When he was in America toward the end of his life he asked to be taken to jazz clubs, where he would sit and watch pianists and take notes.
Bartók had superhuman sensory ability. He could hear sounds that no one else could hear in the stillness of midnight deep in the forest. The faint sounds of leaves and tiny nocturnal creatures. He composed whispers of music based on these subtle sounds and called it "night music." One night at a rural retreat in Vermont someone's cat was lost. From the house he could hear the cat, and he led a search party deep into the woods right to the tree which the cat had climbed up but couldn't get down. While there, he dug his hands into the carpet of decaying pine needles and contemplated aloud this amazing substance "composed of equal portions of life and death." He was acutely sensitive to the natural world that way.
I also think he was the sexiest man who ever lived. Those eyes... *swoon*
My favorite piece by him is something I'm practicing on the piano: "Six Dances in Bulgarian Rhythm" - the concluding portion of Mikrokosmos. Playing these intricate jewels on the piano intrigues me no end. The first one is a 9/8 Turkish karsilama rhythm that builds to a thunderous crescendo. The third one is in the style of Gershwin. The rhythm in the final one is like a furious Afro-Cuban 8, a familiar rhythm to rock-n-roll fans and the piece totally rocks. Bartók dedicated the "Six Dances" to a woman pianist, Harriet Cohen. I play them to commemorate her for first bringing this amazing music to people's ears.
And in Concerto for Orchestra he made clarinets and flutes laugh. It sounded like something you'd hear on a Looney Tunes soundtrack from around that time.