"It is the characters that make a game great..."
Cloud Strife:  The sometimes confused hero of FF VII.  A memeber of SOLDIER, a specialized mercenary unit, he is a loner at the beginning of the game.  Part of a strange love triangle with Tifa and Aeris.
Tifa Lockheart:  This sweethearted yet tough young lady runs the Seventh Heaven bar.  She has major feelings for Cloud, and is part of the triangle including Aeris. 
Aeris Gainsborough:  A simple flower girl (the source of one of the most quoted scenes I've seen from any FF, including an appearance in Tactics), Aeris is so much more.  A part of the love triangle involving Cloud and Tifa.
Barrett Walace:  Leader of Avalance, he hates Shinra with a firey passion.  He had a gun grafted on to his arm, making him more than a formidable force in combat.  His hometown of North Corel was torched by Shinra.
Cait Sith:  There's nothing quite like a cat riding a giant Mog.  He joins you at first because he's working for Shinra, but then he has a Moment of Conscience.  Just plain weird looking.
Cid Highwind:  7's version of Cid.  Very reminesent of 4's Cid (he even stole the guy's goggles).  Master aviator, wannabe space boy.  He becomes somewhat bitter about a failed launch attempt that would have put him into space.  Oh well, turns out he shouldn't have been anyway.
Vincent Valentine:  The Man (Sorta) With the Golden Hand.  After confronting Hojo for experimenting on Lucrecia's child and losing, he's turned into and undead.  Really quiet by the time the party picks him up, he's only along to get rid of Sephiroth.
Yuffie Kisaragi:  Just a touch of a cleptomaniac, she can't keep her hands off materia.  A little on the ditzy side, but still a strong combatant.  She's run away from home because she doesn't agree with the way her father's running things.
Sephiroth
This game would not be what it is wihout him.  As one who's more knowledgeable than I on the subject said, "It's a shame, really - if he'd never met his real mother, he might have been quite a nice guy." (Daniel Orner of the FF Compendium)  From my searches on the vast net, I've seen more pages dedicated to him than any other character.  He is kind of doomed to a fate of evil; I mean, his father is a sick and twisted medical genius who experiments on anything he can, and his genealogical mother is an earth destroying entity.  And we complain because our parents "just don't understand us." 
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