(n.) One who refuses or rejects.

anomaly bitter-ender brawler crosspatch defeatist defendant denier diehard disputant dissenter dissentient dissident freak individualist inner-directed person intransigent irreconcilable last-ditcher litigant misfit negativist nonconformist noncooperator objector obstructionist obstructive oddball opposer oppositionist pessimist plaintiff prophet of doom protester quarreler refuser resister sceptic scrapper sport wrangler