adamant, adamantine, bullheaded, dogged, hard, hardened, hardheaded, hard-nosed, headstrong, immovable, implacable, inconvincible, inflexible, intransigent, mulish, obdurate, obstinate, opinionated, ossified, pat, pertinacious, perverse, pigheaded, self-opinionated, self-willed, stiff-necked, stubborn, unbending, uncompromising, unrelenting, unyielding, willful(or wilful)

anal-retentive, obsessivewayward, wrongheadeddetermined, hell-bent, inexorable, persistent, relentless, resolved, set, single-minded, steadfast, stouthearted, tenacious, unflinchingfirm, hard-line, hard-shell(or hard-shelled), iron, severe, stern, stricthidebound, narrow-minded, rigidbloody-minded(chiefly British), cantankerouscontrary, cussedcontumacious, disobedient, froward, insubordinate, intractable, recalcitrant, refractory, uncooperative, ungovernable, unmanageable, unrulydefiant, insurgent, mutinousindomitable, invincible, unconquerableconfirmed, inveterate, unregeneratedemanding, exacting