Originally a mild-mannered boy from Nibelheim, Cloud begins the game as a mercenary hired by the rebel group Avalanche in order to take down the planet-harvesting megacorp, Shinra. Cloud boasts of his past as a member of SOLDIER, an elite group of genetically-infused warriors, and possesses an aloof, dismissive attitude toward others as a result - seemingly operating with no moral code other than following the money and being quick to snark.
In truth though, Cloud's actual past is vastly different - the background he speaks of is quite literally not his. His struggles with his memories and identity greatly inform the way he is, and are a great source of psychological anguish for him throughout the game. The true Cloud is an awkward and optimistic soul who cares deeply for his friends - and with their help, he is able to break out of his shell and defeat Sephiroth once and for all.