In the verbal armoury of English party politics in the twentieth century of the Christian Era the term “Die-Hard” has come to be used as a shaft of ridicule to be shot at a politician who makes a parade of his intention of “dying in the last ditch” in defence of some political cause that is patently lost, and this particularly if his opponents have reason to expect that the poseur will prudently resign himself to the inevitable when it actually comes to the point. This latter-day connotation of play-acting does not, however, attach to the sobriquet in its origin. The authentic “Die-Hards” are an infantry regiment of the British Army; and the Fifty-Seventh won their nickname as a title of honour at the Battle of Albuera [in the Peninsular War] in A.D. 1811. In an engagement in which the regiment was being mown down by the enemy’s fire, their commander, Colonel Sir William Inglis, as he fell desperately wounded, cried “Die hard, Fifty-Seventh! Die hard”; and the regiment gained the name of “Die-Hards” for themselves by taking their fallen Colonel at his word.
A Study of History, Vol VI, OUP, 1939 (footnote)