From Peter Jenkins on the Mega Man mailing list:
I remember some discussion in the past where people were trying to decide WHO it was that originally envisioned our fave little hero. All of the names listed in the credits of the N.E.S. games are strange little pun-names, almost nick-names, and offer no helpful insight. Well, in the latest Hyper magazine (which is easily the best gaming mag in Australia) they interviewed a man called Keili Inafune about his upcoming game, Onimusha. (“Ogre Samurai,” is apparently a translation of the title) Anyway, in one of the questions, Hyper say to Inafune-san “You are the creator of Mega Man. To create Onimusha, did you work to some specs given to you, or did you create the game idea and present it to Capcom?”
Perhaps this man is Capcom’s Shigeru Miyamoto – the ideas man… Whether they meant that HE was the person who invented Mega Man or they were talking about Capcom in general is not specifically clear, but still… It turns out that this is actually Inafking, producer of many of the MM games. Considering how many he’s been listed in, it seems pretty likely that he did design MM.