"person having red hair," mid-13c. (1256 as a surname), from red (adj.1) + head (n.). Red (adj.), of persons, "having red hair" is from late Old English. Both Cain and Judas formerly were reputed to have had red or reddish-yellow beards.
The Carrot pate be sure you hate, for she'l be true to no man,
But put her too 't and she will do 't, and oft turns very common:
She that is red upon the head will doubtless ne'r forsake it,
But wanton be, assuredly, and willingly will take it.
["The True Lover's Admonition," Roxburghe Ballads, c. 1680]
Traditional ideas about red-haired people are not complimentary. Physically, they are said to sweat easily, bleed copiously, have a strong foxy smell, and such bad breath that they can raise blisters on other people simply by breathing over them. Morally, they are expected to be 'bad children' who cause nothing but trouble; they will be hot-tempered, treacherous, and highly sexed. The medieval notion that Judas, Cain, and Mary Magdalene were red-heads arose from these beliefs, and helped to perpetuate them. ["Oxford Dictionary of English Folklore," 2000]
As an adjective, "having red hair," from 1660s. Red-headed is attested from 1660s; red-haired from c. 1500.