Overview
Die hard is a phrase coined by Lieutenant-Colonel William Inglis of the 57th (West Middlesex) Regiment of Foot during the Battle of Albuera. Its original literal meaning has evolved to describe any person who will not be swayed from a belief. The metaphorical sense was first applied almost exclusively to right wing politics, but since the latter half of the 20th century, it has come into general use with wide application.
Original military use
The phrase die hard was first used during the Battle of Albuera (1811) in the Peninsular War. During the battle, Lieutenant-Colonel William Inglis of the 57th (West Middlesex) Regiment of Foot was wounded by canister shot. Despite his injuries, Inglis refused to retire from the battle but remained with the regimental colours, encouraging his men with the words "Die hard 57th, die hard!" as they came under intense pressure from a French attack. The 'Die Hards' subsequently became the West Middlesex's regimental nickname.
The term was later used to deride several senior officers of the Army who sought to maintain the system bequeathed to them by the Duke of Wellington and who strenuously resisted military reforms enacted by Parliament starting in the late 1860s.
British political uses
From Wikipedia (CC BY-SA 4.0).