pertinacious

deaf diligent doctrinaire dogged hard-nosed/hardheaded hardheaded importunate incompliant indefatigable indomitable intractable intractable/intransigent more diligent more hard nosed more hard-nosed more hardheaded more hardheaded more hardnosed more intractable more intractable more intransigent most hard-nosed most hard nosed most hardheaded most hardheaded most hardnosed most intractable most intractable most intransigent obstinate peevish persevering persistent relentless stiff stubborn tenacious unbendable uncompliant untiring unyielding willful