Cloud (story focuses around his past and present with other characters)
President Shinra (things would not be what they were or as bad)
Jenova (It's her fault for causing trouble with Sephiroth)
Hojo (yet it is mainly his fault for wanting to bring back the ancients)
Sephiroth (he went mad...and is the main baddie)
Rufus (a huge bad seed and antagonist for Cloud)
Barret (Cloud wouldn't have had a job if it wasn't for him)
Vincent (he knows alot about Sephiroth and why things are like they are in the game, plus his limit break is nice)
Cid (yeah...the airship does come in handy)
Reeve/Cait Sith (he also knows alot)
Lucrecia (there would be no Sephiroth without her)
I could go on and on but I'll stop there.