The man we are presented to at the start of this game is self-centred, selfish, aloof, and also fairly greedy person. He has no interest in helping the Planet, Shinra, or really doing anything other than lining his wallet with some nice gil with some easy jobs.
"I don't care what your names are. Once this job's over... I'm outta here."
Cloud spends the majority of his time with Avalanche treating them very, very poorly. He tries to remain cold and distant, but some game dialogue shows that his fellow Eco-terrorists have seen through his cool-guy facade and have started to assume that he really just has no idea how to be a friend. Which isn't too far off from the truth.
This persona is actually ever changing throughout the game. It doesn't remain static. One strong example is when he meets Aerith, when he switches from being a flippant jerk to a rather charming gentleman. Given that Zack told him this story and all of these memories are in his head somewhere, it makes sense that he'd play the roll that Zack did. The more Cloud goes through, the more it morphs to fit the scenario. While he is at first nothing but rude and short, given that he's running off of Tifa's memories, his idolization of Sephiroth who was 'aloof and cold', and Zack's determination - he's really just putting up a front. Throughout his time in Midgar, he is as rude and to the point as possible.
But, if Cloud sets his mind to do something, it will be done. Dressing up in drag to save Tifa? No problem, he'll go all out to be the best possible woman. No matter what consequences might crop up. Even when faced with the most dire of circumstances he doesn't back down, instead rising to the challenge and fighting his way through. He may not always like it, and he may act put upon, but he's a reliable warrior and earning his trust is a surefire means of gaining an excellent warrior and a trusted friend.
"Gotta admit he was a strange
dude. Just when you thought he was smart, he'd show how stupid he was. Everything about him from his movements is his speech were kinda odd."
Cloud is not confident. He is not brave. He isn't a great hero. The torture and experiments he went through in Nibelhiem shattered his already fragile mind. Given the proper time, it's possible he could have recovered and regained a proper sense of self... but that's not how things went. Cloud was left on his own and had the choice either to die, or to become a stronger person to keep himself alive. It sounds like a good thing, right?
But that's where we start hitting problems.
Though he thinks he is, in the end he's simply mimicking a great man. All of the things that he believes he's accomplished are actually the achievements of someone else. Though Cloud tries to walk the walk and talk the talk, he's only going on what he's heard and so everything falls flat and looks a little strange. Everything from the way he moves to the way he speaks belongs to another person - not all exactly the same person, but rather a mismatch of people Cloud admired and his misconceptions about how a SOLDIER 1st Class would act. So, Cloud has big, gaping holes in his memories. And along with that, he knows things he shouldn't know and doesn't know things he should. All in all, he's a very strange person to watch and talk to.
Of course, given that he's not cold-hearted or a monster, the loss of the people he worked with hits him hard. The betrayal of ShinRa doing that to their own people stings.
