Other forms: diehards
A diehard is a person who likes things a certain way and doesn't want them to change — or who sticks to an opinion no matter what. If everyone in your family is a Democrat except your cousin, you might call him a Republican diehard.
A diehard will hold fast to her ideas, views, or opinions even in the face of opposition. You could call yourself a diehard if you insist on sticking to the same recipes for Thanksgiving dinner that your grandmother always made, especially if your siblings keep lobbying to add new dishes to the menu. The word diehard dates from the 19th century, and it originally referred to a tough soldier in a certain British Army regiment.