unbendable

adamant adamantine balky brassbound bullheaded cantankerous contumacious cussed determined die-hard dogged firm fixed grim hardheaded headstrong implacable incompliant inexorable inflexible insubordinate intractable intransigent iron mulish obdurate opinionated ornery persevering persistent pertinacious perverse pigheaded rebellious recalcitrant refractory relentless remorseless rigid self-willed set in one's ways single-minded steadfast stiff-necked tenacious tough unbending uncompliant uncompromising unmanageable unreasonable unrelenting unshakable untoward unyielding willful