A reference to anybody who is resistant to any kind of change, and reluctant to give up his or her beliefs, positions, or attitudes: They were diehard politicians who were locked into their uncooperative ways.

Dina's father was a diehard Republican and her mother was a diehard Democrat and neither one could agree on what should be done politically.

Strongly or fanatically determined or devoted to attitudes and behaviors that are stubbornly adhered to; such as, an outdated view or an unreasonable position: Agustin's die-hardism made it impossible for his fellow workers to develop any new techniques for doing the job.