Same word as obstinate:

adamant, cantankerous, contradictory, contrary, contumacious, convinced, dead set on, dogged, dogmatic, firm, hard, hardened, headstrong, heady, immovable, indomitable, inflexible, intractable, intransigent, locked in, mulish, obdurate, opinionated, opinionative, persistent, pertinacious, perverse, pigheaded, recalcitrant, refractory, relentless, resolved, restive, self-willed, steadfast, strong-minded, tenacious, unalterable, unflinching, unmanageable, unyielding, willful