A reserved young man who brandishes a large sword with ease. He leads his other warriors with his rational decision-making befitting a leader, but internally he has difficulty being confident in his actions.
An acerbic young swordsman with glowing eyes who wields a blade as large as he is.—Dissidia Final Fantasy description
SOLDIER is Shinra’s elite paramilitary unit, of which Cloud was never a top-ranking member. At the beginning of Final Fantasy VII, he works as a mercenary-for-hire for anti-Shinra organization AVALANCHE.
He learns of the truth later on in the game. He and his friend SOLDIER 1st Class Zack Fair underwent Professor Hojo’s experimentation. When Zack broke out with Cloud, the latter suffered a severe case of Mako poisoning. A broken Cloud assumed Zacks memories as his own, and the physical and psychological trauma was enough to annihilate his personality.
Like Terra and Tidus, Cloud in on Chaos’ side in World B. This is likely due to Sephiroth’s influence, as Cloud contains the same Jenova cells present in the former’s body. Also, Cloud knows and protects Tifa from Sephiroth, much like he did during the Nibleheim Mako Reactor mission. He fights to end the cycle in order to save her.
Yet, when does Cosmo call Cloud to World B? At the end of Final Fantasy VII, Cloud can follow Sephiroth mentally through the Lifestream. Perhaps anytime Cloud suffers a flashback or mind warp, he transports to World B. Or perhaps he arrives at World B after falling from the Sector 5 Reactor Platform.
One likely scenario is during one of his mental breakdowns. Cloud falls into the Lifestream and surfaces on Mideel’s shores. He’s suffered intense Mako poisoning, again, and as a result is incoherent. He happens upon even worst luck, as Ultimate Weapon attacks Mideel. After destroying the ground, Cloud and Tifa fall into the Lifestream.
However, considering his guilt, depression, and insistence on doing things alone, Cosmos might have called Cloud during the events of Advent Children.