fanatic
— Adjective
– English
~ marked by excessive enthusiasm for and intense devotion to a cause or idea; "rabid isolationist"
fanatic
— Noun
– English
~ a person motivated by irrational enthusiasm (as for a cause); "A fanatic is one who can't change his mind and won't change the subject"--Winston Churchill
fanatical
— Adjective
– English
~ marked by excessive enthusiasm for and intense devotion to a cause or idea; "rabid isolationist"