Guardians are some of the most formidable enemies in The Legend of Zelda: Breath of the Wild, but they were originally designed to destroy Calamity Ganon, not stop Link. The machines were built by the Sheikah, who hail from Kakariko Village, and by the time BOTW takes place, the Guardians are roughly 10,000 years old. The Guardians actually succeeded in their original purpose, but the unforeseen eventuality of a Second Great Calamity and the preparedness of Ganon resulted in the ancient machines turning on the defenders of Hyrule.
BOTW takes place in the far future of an unspecified Legend of Zelda timeline split, where the Sheikah Tribe had once grown into a prevalent and highly developed culture. In previous games, the Sheikah were mysterious and rarely seen, yet frequently involved in saving Hyrule from the machinations of Ganon. In what is considered ancient history to the characters of BOTW, however, the Sheikah were the designers of advanced technology, whose inventions would play the largest role in rebuffing Ganon's attempted conquest.
Related: Why Ocarina Of Time's Ganondorf Is So Different From BOTW's
The Sheikah would eventually fall victim to their own creations, alongside the rest of Hyrule. The Guardians were unexpectedly consumed by Calamity Ganon's malice, and seem to be a major contributor in the kingdom's utter destruction. Castle Town was razed and the denizens of Hyrule were cloistered into isolated communities while Zelda contained Ganon himself for a century. The Legend of Zelda's Sheikah Tribe, once great in BOTW's history, withdrew into Kakariko Village and even splintered, resulting in the rise of the militant Yiga Clan.
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