dogged

Synonyms: adamant bullheaded firm hanging tough hardheaded hard-nosed indefatigable inexorable inflexible insistent mulish obdurate obstinate perseverant perseverative persevering pertinacious pigheaded relentless resolute rigid single-minded staunch steadfast steady stubborn tenacious tough nut unbending unflagging unshakable unyielding

Antonyms: indifferent irresolute undetermined yielding