Karlheinz Stockhausen (1928-2007)
Stockhausen always made a strong impression on me, and I'm sorry to hear of his passing. My friends and I in college would listen to Gesang de Jungelinge over and over. Most recently I downloaded Gruppen from the DG Webshop and enjoyed the Harmonia Mundi release of Stimmung out this fall. Several of the days from Licht are also among my favorites despite the odd views of the man, Stockhausen's music was excellent and creative.
News of his death via The Rest is Noise.