What was Sephiroth in disc 1?

[Raistlin]

I remember a popular debate in the first few years after FFVII came out was what exactly you were chasing during disc 1, when the real Sephiroth was trapped in solid mako. Was it a clone? Was it a ghostly image of the real Sephiroth? Was it Jenova?

None of these answers seemed to adequately explain everything that went on during disc 1. IIRC, the Sephiroth you chased seemed to be able to throw Jenova at you whenever we felt like, was able to float and disappear through walls (as in the Temple of the Ancients), but was also seen with a number on his hand (by Dio at the Gold Saucer). Which tells us... a whole lot of contradictory nothing.

So what do you think Cloud and his posse were tailing for most of the game?

[Shorty]

I always thought it was Jenova pretending to be Sephiroth. I guess that I had never considered that it could be clone, though!

[Sephex]

Jenova cells combining with various clones. Simple as that. He could posses people like that one movie where Denzel Washington gets screwed.

[Rostum]

I had thought it was Jenova for quite awhile, but I thought I read that they confirmed it to be Sephiroth manipulating Jenova?

[escobert]

I always thought it was Jenova pretending to be Sephiroth. I guess that I had never considered that it could be clone, though!

Yeah I figured it was this, or a clone of some sorts.

[ReloadPsi]

I had thought it was Jenova for quite awhile, but I thought I read that they confirmed it to be Sephiroth manipulating Jenova?

The Ultimania confirmed it. Personally I found a hell of a lot more of the game making sense after I read that. The full translation's on GameFAQs if you care to check it out; there's an interesting tidbit that in my opinion explains why Hojo took his vacation to Costa Del Sol when he did. See if you can figure it out

[Del Murder]

Always Jenova for me, but controlled by the real Sephiroth at the crater.

[Goldenboko]

My personal interpretation of the game was that Jenova had poisoned and manipulated Sephiroth and that by the end of the game even with Jenova destroyed/killed Sephiroth was still carrying out her will (because he pretty much was), but the Ultimatania guide pretty much reverse the who's who in my interpretation.

I think that ultimately looking for deep meaning in why Sephiroth was doing what he was doing is the wrong way to go about looking at this game. Sephiroth went nuts and I think that should be the ends end of why he started trying to kill everyone, his goals are ultimately unimportant, he's just a crazy dude.