quote

A malevolent alien, with an instinct to cause ruin, that crashlanded upon Gaia over 2000 years ago. Despite it almost causing the extinction of the Cetra race, it was eventually sealed within a geological stratum.

However, one day Shin-Ra discovered the creature and, falsely believing her to be a Cetra (Ancient), used her cells in the experiment that helped create the ominous Sephiroth. They were also used by Professor Hojo for his own experiments, which included Cloud & Zack.

Neoportal

Jenova is an alien life force, and that is about all that is detailed to us. It's a parasitic force that is able to be seperated and still manage to live and survive, keeping its mind in a tangible state. What its purpose is, is really unknown.

It's purpose was to basically destroy every planet.
But the Cetra improsoned it in a rock, it went into a coma, etc. etc. etc.

The Cetra imprisoned it in a rock? I thought it fell from the sky as a meteor, and thus created the North Crator. I've not heard anything about the Cetra imprisoning it. Infact, it killed the Cetra off, did it not?

Yeah, when Hojo and Gast found Jenova she was in a geological stratum of 2000 years (a 2 thousand year old rock)
The Cetra put her in there.

I thought that the Centra fought it untill it became weak. Then they just buried it or something. And then a long long time later, Shinra scientists discovered it. Im sure i dont remeber about it being in a rock... I thought that they found it at a source of Mako.

Yeah, they never said anything about it being sealed by the Cetra.

The game does not give much information on Jenova, (which in itself should quash the entire "Jenova controlling Sephiroth theory", but some people...) yet in the video which can be accessed from Gast's old home at the Snow Village, Ifalna discusses Jenovas impact on the Cetra in brief. Apparently, the WEAPONS were created by the planet in order to destroy/imprison Jenova, but before they could be used, a few surviving Cetra managed to defeat
Jenova and seal her in some sort of rock formation.
As for Jenova's purpose? Again, not much can be discerned from the game script itself, but I'd imagine* that it was simply to find the Promised Land, and to summon Meteor. Whether she wished (or even knew how!) to become one with the planet back then, or wished simply to destroy all life on the planet, I won't even hazard a guess at...

*Feel completely free to disagree with me here, as I'm just brainfarting tbh...

destroying all life would be a pretty pathetic motive
I assumed it was to be like a leach to the planets core, draining it, some of this will rubbed off on sephiroth who wanted to become one with the planet

quote Vindiction

destroying all life would be a pretty pathetic motive

hmm though ff7 did have alot of cliché's the game prided itself on its villians.
Sephiroth was not evil, he was just driven mad by jenovas will etc etc... I always though of Jenova as a leech, it seems right....

"she is an alien who fell to the Planet from space, and tried to take over the world by gaining control of the Lifestream. She befriended the Cetra at first but then spread a virus which turned most of them into monsters, but a few survived and managed to seal her away within the Planet. Two thousand years later, Professors Gast and Hojo find Jenova's body and mistakenly believe it to be that of a true Cetra. Fortunately for her, this meant that she was released from the geological stratum in which the Cetra had sealed her."

quote Miller

"she is an alien who fell to the Planet from space, and tried to take over the world by gaining control of the Lifestream."

quote Sephiroth

Mother was destined to become the ruler of the Planet

I had always thought of Jenova as being frozen in a rock like substance... I got the impression that it was found in the North Crater, and therefore was likely frozen. I also got the impression that Jenova was like a parasite, hence how it infected the Cetra with a virus, and maybe it's tie to the lifestream is to feed off of it... Just my thoughts here.

quote Chaos_Vincent

I got the impression that it was found in the North Crater, and therefore was likely frozen.