die-hard (n.)

also diehard, 1844, in reference to the 57th Regiment of Foot in the British Army, from the verbal phrase die hard "suffer, struggle, or resist in dying," 1784; see die (v.) + hard (adv.). As an adjective, attested from 1871. The  brand of automobile battery, spelled DieHard, was introduced by Sears in 1967.