A "tenacious fighter" refers to someone who is extremely determined, persistent, and doesn't easily give up in a fight or struggle. They keep pushing forward even when facing difficulties or opposition. Full definition
«Attorney General Eric Schneiderman has been a tenacious fighter for working people across the state; and his work on recovering wages for workers in the car wash industry has been particularly remarkable,» said RWDSU President Stuart Appelbaum. (nystateofpolitics.com)
Clinton's campaign will air the first two TV ads of the Democratic primary race tomorrow, as part of an effort to head off Republican attacks and present Clinton as a «tenacious fighter» for everyday Americans. (nystateofpolitics.com)
This dog is courageous and a tenacious fighter if provoked. (europuppy.com)