adjective

having or showing tenacity and grim persistence.

success required dogged determination

tenacious,determined,resolute,resolved,purposeful,persistent,persevering,pertinacious,relentless,intent,dead set,single-minded,focused,dedicated,committed,undeviating,unshakeable,unflagging,indefatigable,untiring,never-tiring,tireless,unfailing,unfaltering,unwavering,unyielding,unbending,immovable,obdurate,strong-willed,firm,steadfast,steady,staunch,stout-hearted,laborious,perseverant,indurate