10,100 years before the events of Breath of the Wild, Ganon broke free of the seals restraining him, and with the energy of Malice became Calamity Ganon. The people of Hyrule utilized their advanced level of magic and technology to aid the Hero chosen by the Sword that Seals the Darkness, as well as the Princess blessed with Sacred Power.
As part of their efforts, they created the Divine Beasts, massive magical constructions endowed with tremendous power, each piloted by a champion of Hyrule. The four champions had each been blessed by the Goddess Din in some way; it was this connection with the Triforce of Power that enabled them to turn some of Ganon's own power against him, using the Divine Beasts to restrain him.
Vah Rudania was piloted by Dinah, a Hylian knight blessed by Din. Dinah's sacred mission was to restore the honor of the Goddess of Power, whose Triforce had been so misused by Ganon. In her pursuit of power quite literally for Power's own sake, though, she struggled with the same subtle seductions that turned Ganon itself to evil.
Vah Rudania's primary AI core, Lah Rudania, was somewhat temperamental and prone to glitches, for some reason. While each of the Divine Beasts' brains were capable of separating in a pinch, Lah Rudania was particularly independent, and had actually sought out Dinah when the Sheikah technicians took too long to find her themselves.
Vah Naboris was piloted by Ignatius, a Hylian who had been blessed - or cursed - as a conduit of Din's great fire. He struggled to understand the source of this unique power - as did the Cult of Dinraal, a secretive order of Wizzrobes who wanted nothing more than to capture him and steal his power.
Vah Medoh was piloted by Grik, a Sheikah survivor of a lost dungeon. He had gotten trapped in the dungeon while being sought as a pilot for the Beasts, and while the monsters inhabiting the dungeon took his left arm, he found at the core of the dungeon an ancient sword of the Royal Family, which seemed to choose him as its wielder.
Vah Ruta was piloted by Bo, a farmer who stubbornly refused to accept the title of "Hero" - "I'll help you out just the once, but afterwards I'm going back home to my family, thank you very much." While he sometimes struggled to make full use of the advanced magic and technology at his fingertips, the other champions knew him as a true hero who would help them through thick and thin… even if he'd grumble about it the entire time.