Fierce or resilient

He's a real die-hard. He never gives up until he succeeds

È un tipo duro a morire, non si arrende mai finché non la spunta

Old prejudices always die hard

I vecchi pregiudizi sono sempre duri a morire

The die-hards were the British 57th Foot Regiment, so called because their Colonel Inglis addressed them before the victorious battle of Albuera against Napoleon's French on May 16th, 1811, "Die hard, my lads, die hard." Only one officer of 24 survived, and only 168 men of 584