It’s hard to leave any discussion around the development of synth as an instrument without mentioning Tangerine Dream and Popol Vuh, but they were arguably more related to the prog-rock scene than as composers.
Incidentally, a former member of TH, Klaus Schultz also died last month. TG didn’t land any major soundtracks (like Jarre or Vangelis), but they were nonetheless highly influential , if only due to their prolific releases.