Who is the 'grey voice'?

[General-Beatrix]

It is actually Jenova. This happens because Cloud was injected with Jenova's cells. It is clearly given away when it says something (cant remember what) at the part where Aeris dies.

Wouldn't Jenova then try to mess with his mind?

[Ohhh]

Come to think of it, didnt (if the grey voice is jenova) she try to mess with his head at the promised land when hojo was talkin to him and cloud was floating around in the air?

It would make more sense for it to be the "real" cloud talkin to him... by the way there is no clone of cloud is there? because at one point (at the promised land) he tells Tifa "Im sorry. I hope one day you can meet the real Cloud" so does that mean... omg im spinnin myself out *shuts up*

[nik0tine]

It's Red XIII. His race is telepathatic.

This is correct.

[sayen]

the voice is jenova when. aeris dies jenova/sephiroth goes "because you " then after the jenova death fight jenova says "are a puppet". at north crater jenova is controlling cloud because cloud dosent know he can float/flie like sephirtoh/jenova can.

[Squall of SeeD]

It's not JENOVA or Sephiroth. They -- or at least Sephiroth -- would want to destroy Cloud's mental stability, not reinforce it, which is what his subconscious wanted. The voice tells him to do things like ask Tifa about what happened five years ago. It wanted him to remember the truth. Remembering the truth made his mind stronger, something Sephiroth wouldn't want.

The voice is his subconscious. This has been proven beyond all argument:

http://www.geocities.com/ff7analysis/Voice.html