obstinate, dogged, pertinacious, strong-minded, strong-willed, refractory, dour, difficult, hardheaded, unyielding, more...

flexible, pliable, malleable

mulish, obstinate, headstrong, cussed, contrary, willful, unyielding, dogged, more...

strong headed,   not compromising,   unwilling to accept,   hard to convince,   not changing mind,   set in your ways,   not easily removed,   difficult to remove,   obstinate folk,   adamant person