The voice

[Castiroth]

Ok on disc 1 when your in junon after you save prisila and you go to the old womans house and fall asleep. Who is that talking to cloud ive completed the game a good few times and i still aint got no clue who it is i was thinking Sephiroth then i thought jenova then i thought it was the "real" cloud now i dont know what to think plase help

[Chris]

I'm not exactly sure, but I'd bet my bottom dollar that it's the "Real Cloud".

[Castiroth]

I thought it was the "real cloud" after i thought it was Sephiroth cause*SPOILER* when u go to the crater after climbing great glacier sephiroth wants the "real cloud" back so then i thought it was sephiroth damn confusing i think

[Squall of SeeD]

I believe it's Cloud's subconscious. Here's something I wrote on the matter some time ago:

_______________________________

The voice was certainly Cloud's subconscious.

At one point the voice tells Cloud to ask Tifa about what happened five years before:

(At Junon.)

"...That reminds me."

"You again?"
"...Who are you?"

"...You'll find out soon. ......But more importantly,
5 years ago..."

"5 Years ago... Nibelheim?"

"When you went to Mt. Nibel then, Tifa was your guide, right?"

"Yeah.... I was surprised."

"But where was Tifa other than that?"

"...I dunno."

"It was a great place for you two to see each other
again."

"...You're right."

"Why couldn't you see each other alone?"

"...I don't know. I can't remember clearly..."

"Why don't you try asking Tifa?"

"...Yeah."

"Then, get up!"

"Hey wake up. Wake up, Cloud!"

It would have been detrimental to JENOVA's/Sephiroth's plans to tell Cloud to do this, as it was Cloud's fragmented psyche that allowed him to be weak enough to control. Learning the truth would cause him to have to piece the past together and become "fixed," possibly solidifying his sense of self and his mental fortitude, which would make him mentally stable enough to resist JENOVA's/Sephiroth's control.

Note that at the Reunion, JENOVA/Sephiroth makes a point of trying to cause Cloud to question himself, breaking down all confidence in his sense of self that remained, and, thus, making him vulnerable to control at the crucial moment of handing over the Black Materia.

While it would have been a hindrance to what JENOVA/Sephiroth had in mind for Cloud to learn the truth at that point, as it would have strengthened his mental fortitude, it would have done exactly what Cloud's subconscious wanted. When his subconscious speaks with Tifa in the Lifestream, it's trying to help Cloud learn about the truth of his past, the same as the voice telling him to ask Tifa about Nibelheim no doubt must have been, for Cloud's mind would have been stronger had he known the truth of his past, and he would have possibly been able to fend off JENOVA/Sephiroth's control.

Note also that at an earlier time than when the voice spoke to Cloud, it tried reminding him of a time that had taken place five years before in an effort to try to get him to remember the rest of it which didn't come until much later and with Tifa's help:

(While sleeping at Aerith's house)

"...seem pretty tired......"

Cloud
".......!?"

"I haven't slept in a bed like this ....in a long time."

Cloud
"....Oh, yeah."

"Ever since that time."

[The scene fades in to Cloud's house in Nibelheim.]

"My, how you've grown."
"I'll bet the girls never leave you alone."

Cloud
"...Not really."

"...I'm worried about you."
"There are a lot of temptations in
the city..."
"I'd feel a lot better if you just
settled down and had a nice girlfriend."

Cloud
"...I'm all right."

"You should have..."
"an older girlfriend, one that'll take care of you."
"I think that would be the perfect type for you."

Cloud
"I'm not interested."

[The scene fades back in to Aerith's house.]

That Cloud remembering the truth of his past would have been detrimental to JENOVA/Sephiroth's plans to use Cloud completely disqualifies it/him/them from having been the voice. Further still, JENOVA/Sephiroth doesn't even recognize Cloud on the Shin-Ra Cargo Ship, and Cloud had been experiencing the voice episodes for a while before that point:

"........After a long sleep..."
"...the time..."
"...time has....... come....."

Aerith
"Look, Cloud!!"

[The form of Sephiroth rises up through the floor where the captain's body had been standing.]

Cloud
"Sephiroth! You're alive!"

"........Who are you?"

Cloud
"You don't remember me!? I'm Cloud!"

"Cloud..."

Cloud
"Sephiroth! What are you thinking!? What are you doing!?"

"...the time..... is now......"

Something else to consider -- and that is perhaps the greatest piece of evidence toward this possibility -- is that in the Honey Bee Inn's &$#% Room, Cloud actually encounters his subconscious (in the form of his younger self) and speaks with it briefly:

[Cloud enters the room and a bright flash occurs. A translucent form of his younger self his before him.]

Cloud
"Hmm.....? You.....?"
"What are you doing in a place like this?"

[Cloud clutches his head.]

"That's what I want to ask you. Should you be foolin' around
here?"
"You think problems will go away just thinkin' about them?"

[The younger form of Cloud rises and flies forward into Cloud's body.]

"Oh no!"
"Help! Someone...! Hurry!"

"You can't change anything by just sitting back and looking at it."

Cloud
"What are you saying?"

"It's started moving."

Cloud
"What has?"

"Wake up!"

Note particularly that the double of Cloud in the Honey Bee Inn is a younger form of him, just as the form of his subconscious was in Cloud's mind when Tifa helps him piece his past together, and note also that this younger form called to him to stop when he was handing the Black Materia over to Sephiroth at the Temple of the Ancients:

Linkage 1.
Linkage 2.

It is with this same younger form of Cloud that the other transparent forms of him fuse once Tifa has helped Cloud regain his past in the Lifestream. After that, the adult form of him that was hanging overhead fused with the younger form. Beyond this point, there ceases to be any voices in Cloud's mind as there had been before.

Finally, consider that in the game's ending, when we're shown the mental battle with Cloud, the double that rises out of him is an adult at that point, rather than a child, and Cloud was then easily able to either fend off JENOVA/Sephiroth's mental assault, or purge his mind of its/his/their influence as the case may be. This was after the child form of Cloud's subconscious had fused with the adult form in the Lifestream.

While it has been argued that Zack was the voice which Cloud heard, we're given no indication that this would be so, nor is there any logical reason as to why Zack would have been the voice. Zack had been killed by Shin-Ra soldiers before Cloud ever began hearing the voices, and there's no logical reason as to why Zack's Spirit Energy would not have returned to the Lifestream, instead hanging around to speak to Cloud, nor is any indication given pointing toward Zack being the source of the voice.

The only logical conclusion that can be drawn -- and the only one with actual support within the story -- is that the voice was none other than Cloud's subconscious, attempting to get him to recall the truth of his past.

[Castiroth]

hey thanks alot now i can sleep (....no you cant) hey who are you lol

[Masamune·1600]

Who are You? Who am I?

Well, music jokes aside, I have to agree with Squall's analysis and assessment of the situation(s). The voice is, in all likelihood, Cloud's submerged self. There is another dialogue segment that I feel almost certainly implies this.

After falling to the Church after the battle with Airbuster (immediately before first extended conversation with Aeris):

???: ......You all right? ......Can you hear me?

Cloud: ......Yeah......

???: Back then...... You could get by with just skinned knees......

Cloud: ......What do you mean by 'back then'?

???: What about now? Can you get up?

Cloud: ......What do you mean by 'back time'? ......What about now?

???: ......Don't worry about me. You just worry about yourself now.

Cloud: ......I'll give it a try.

Note that 'The Voice' makes reference to "getting by with skinned knees." When Tifa finally helps Cloud unravel his memories in the Lifestream, one of the Clouds mentions that when Tifa fell at Mount Nibel, he only suffered scarred knees. Tifa's injuries were far more severe.

Kid Tifa: ...I wonder if there's anything beyond that mountain?

Kid: Mt. Nibel is scary. Many people have died there. No one crosses that
mountain alive...

Kid Tifa: How 'bout those that died? Did mama pass through the mountain? I'm
going!

Shadow Cloud: I don't remember the path I walked. Tifa missed her step. I ran to
her... but didn't make it in time. Both of us fell off the cliff. Back then, I
only scarred my knees but......

Needless to say, that particular memory was one critical to Cloud's rediscovery of self.

[Big D]

Yup, it was - as has been expertly stated already - Cloud's true identity trying to help him overcome Jenova's influence.

Some people say that Cloud's actually a weak character and not a good hero at all, because his strength and self-identity came from the Jenova cells within him, and the illusions that were built up in his mind.

However, the fact that Cloud's real identity survived shows that he's got a heck of a lot of courage and determination that's all his own. With help, he was able to shake off the bonds and delusions and re-assert who he really was. And even after going through all that, he continued to fight rather than breaking down and wallowing in self-pity.
THAT is Cloud's real strength, I believe. Fighting for what's right even after his own world was turned upside down and inside out, even after he learned the truth and found that it was even worse than reality.