1690s, American English, variant of hollo (1540s) "to shout," especially "to call to the hounds in hunting," which is related to hello. Compare colloquial yeller for yellow, etc. Related: Hollered; hollering.
1896, from holler (v.); earlier hollar (1825). As a style of singing (originally Southern U.S.), attested by 1936.
He hollered out to surrender our weapons
What was he hollering about?