Boulez and Stockhausen, and assisting Bruno Maderna and Luigi Nono. So here's a neat summary of his work in the genre.
Aspekt (1968) is a dizzying stream of pure electronics and sped up tapes, and Cry Of This Earth (1978) sounds like percussive Stockhausen (eg Zyklus) colliding with electroacoustic Nono, as vocal fragments declaim snatches of revolutionary poetry over the clanging, crashing backdrop. Both a perfectly servicable 15 minutes apiece. This disc saves the most complex work for the end though - 38 minutes of a wonderfully unhinged but tightly planned apocalypse.
Inspired by a fictional work mentioned in a novel by Thomas Mann, Apocalipsis Cum Figuris (1984) stacks together four layers of sound. 'Bodily sounds' (don't worry, not quite Scott Walker Corps De Blah territory) sit on top of a layer of vocal fragments, quoting a variety of sources (De Sade, Marx, the Biblical apocalypse, and many more). RIO (Rock In Opposition) aficionados will be interested by Dagmar Krause's distinctive contributions here. The instrumental sounds are the third layer, and the fourth, representing the devil himself, are, of course, a trio of highly stylized pop singers. Well played, Konrad.
Aspekt/Cry of This Earth/Apocalipsis cum Figuris