(Spoilers)

I read in a magazine that He is an ancient and was originally able to revive Aeris. After she died you were to find the Midgar key and return to the man in the pipe and he would be able to revive aeris, this had to be done before you fought Jenova Death, but this idea was scrapped by squaresoft, although this is only a rumour that i read in a magazine it may not be true.