I mean the first game of the series. It may be that the same person did the rest of the series but i only want to know who did the first one... i just downloaded the OST mistagged :(

Here are the composers according to ocremix... I'd trust them... seeing as music is their thing... Don't know who did what song... that will take some serious web sleuthing!

Composers
Makoto Tomozawa Makoto Tomozawa
友澤眞
Setsuo Yamamoto Setsuo Yamamoto
山本節生
Toshihiko Horiyama Toshihiko Horiyama
堀山俊彦
Yuki Iwai Yuki Iwai
岩井由紀
Yuko Takehara Yuko Takehara
竹原裕子

http://www.ocremix.org/game/mega-man-x-snes/