noun

a person who strongly opposes change or who continues to support something in spite of opposition.

a diehard Yankees fan

hard-line,hardcore,reactionary,ultra-conservative,conservative,traditionalist,unprogressive,dyed-in-the-wool,deep-dyed,long-standing,staunch,steadfast,intransigent,inflexible,immovable,unchanging,uncompromising,unyielding,indomitable,adamant,rigid,entrenched,set in one’s ways,blimpish,true-blue,hardliner,fanatic,zealot,true blue,stick-in-the-mud,gammon,blimp

noun

a person who strongly opposes change or who continues to support something in spite of opposition.

a diehard Yankees fan

hard-line,hardcore,reactionary,ultra-conservative,conservative,traditionalist,unprogressive,dyed-in-the-wool,deep-dyed,long-standing,staunch,steadfast,intransigent,inflexible,immovable,unchanging,uncompromising,unyielding,indomitable,adamant,rigid,entrenched,set in one’s ways,blimpish,true-blue,hardliner,fanatic,zealot,true blue,stick-in-the-mud,gammon,blimp