It’s revealed during the course of the game how Jenova came to be – basically it is an alien being that crashed to the Planet on a meteor thousands of years before the game’s events, where it infected the Cetra, turning them into monsters and sending them mad. The surviving Cetra banded together and defeated Jenova, where they sealed it away deep within the Northern Crater, where it had first landed. However, Jenova wasn’t dead – it was merely in stasis.
2000 years later, the Shinra uncovered it, and mistook it for a Cetra (as it was in a geological strata from that time period). It was only later that Professor Gast, the leader of the Shinra’s Jenova Project (which was set up with the intention of creating humans with Cetra powers, in order to reveal the location of the quasi-mythical ‘Promised Land’ which the Shinra hoped to exploit for their own avaricious ends), discovered Ilfana, a real surviving Cetra who told him the horrifying truth – Jenova was not a Cetra, but the being responsible for the Cetra’s destruction.
But by that stage it was too late – the Shinra were using Jenova to enhance the powers of humans for their SOLDIER special forces unit and thus was far too useful to abandon.
Thus setting the stage for the game’s (and Compilation’s) tragic events.
That’s it in a kuponut shell in any event.
MORE SPOILERS
From how it’s referred in the Compilation and the original game, and how it is actually shown, Jenova seems to be virtually immortal from a cellular level – even Hojo states that even if Jenova is dismembered it’s cells try to recombine and become whole again – what he referred to as the ‘Reunion’. In fact, destroying Jenova actually made things worse – it’s cells diffused into the Lifestream where began to corrupt and assimilate itself into it, causing the Geostigma outbreak shown in Advent Children.
As for who is controlling who, Sephiroth-Jenova or vice versa, has always been kept very ambiguous even in the Compilation,but it seems to be subtlety hinted that Jenova is simply an emotionless, quasi-immortal monster, a fusion of cells with little directive other than to consume life. Sephiroth might be subconsciously influenced by the Jenova inside him, but most of his megalomania is simply an Orpheus complex brought about by an obsession with the fictitious image he has of his ‘real mother’.
That is clearly shown time and time again – he really is acting under his own volition – Jenova has nothing to do with it.
Also, Sephiroth wasn’t encased in ice at the Northern Crater, it was materia he was encased in (or rather, semi-crystallised Mako – hence why Cloud’s arm easily pushes into it when he gave him the Black Materia.
Also:Did jenova always have the ability to shapeshift? It looked like our dead mothers and brothers said Ifalna.
Also:Did jenova always have the ability to shapeshift? It looked like our dead mothers and brothers said Ifalna.
had to look this up but here is you’re answer kind of..
Sephiroth: Cloud… Don’t blame Tifa. The ability to change one’s looks, voice,
and words, is the power of Jenova. Inside of you, Jenova has merged with Tifa’s
memories, creating you. Out of Tifa’s memory…… A boy named Cloud might’ve
just been a part of them.
scene from the whirlwind maze….Apparently sephiroth sort of has a similar ability since he created kadaj, yazoo, and loz after he was defeated in the northern crater, they were fused together from his thoughts…..
In any event, he becomes so deluded that Lucrecia could be standing in front of him with open arms saying ‘MY SON! I LOVE YOU!" and he wouldn’t even acknowledge her as his mother.
It’s been a couple of years since I played the game, so my knowledge may not be correct, but I remember the "Cloud-stealing-Zack’s Persona-crap" being a consequence of a mixture of things? (Hojo’s experiments on the kid which left him pretty much demented for a while, J-E-N-O-V-A’s cells’ "power", the shock/trauma sustained by witnessing his friend’s death helplessly…).
In regards to the not once weeping thing… You might want to replay the game: that bonus scene made a good job of showing Strife trembling and screaming at the sky for the era. And about leaving the body of his friend behind, again, I don’t remember Cloud being in a condition which allowed him to do more than what he did. Hell, even a good deal of that Advent Children movie basically revolves around Cloud blaming himself for a few deaths. He’s not that much of an asshole, not on purpose, at least.