Middle English bor, from Old English bar "boar, uncastrated male swine," from Proto-Germanic *bairaz (source also of Old Saxon ber, Dutch beer, Old High German ber "a boar"), which is of unknown origin with no cognates outside West Germanic.
Originally of either wild or tame animals; wild boar is from c. 1200. The chase of the wild boar was considered one of the most exciting sports. Applied by c. 1300 to persons of boar-like character.