they (pron.) Look up they at Dictionary.com
c.1200, from Old Norse þeir, originally masculine plural demonstrative pronoun, from Proto-Germanic *thai, nominative plural pronoun, from PIE *to- (see that). Gradually replaced Old English hi, hie, plurals of he, heo, hit (see he, she, it) by c.1400. Colloquial use for "anonymous people in authority" is attested from 1886.