We should always be grateful to one who has suffered for a great cause.

One word substitute is Martyr.

Fanatic: a person filled with excessive and single-minded zeal, especially for an extreme religious or political cause.
Martyr: a constant sufferer from (an ailment).
Devotee: a person who is very interested in and enthusiastic about someone or something.
Patriot: a person who vigorously supports their country and is prepared to defend it against enemies or detractors.