diehard
nounUK /ˈdaɪ.hɑːd/
US /ˈdaɪ.hɑːrd/
A diehard is someone who never gives up on what they love.
My grandpa is a diehard fan of that old baseball team.
OTHER MEANINGS
2. Refusing to change your beliefs or habits, no matter what.
She is a diehard supporter of the old way of doing things.
3. A person who holds firmly to a cause even when it seems lost.
The diehards stayed until the very end of the meeting.
4. Stubbornly persistent or resistant to change.
His diehard attitude made compromise impossible.