A crusader for a cause is someone who does a lot in support of it.
例句
He has set himself up as a crusader for higher press and broadcasting standards.他自認是一位追求更高的新聞和廣播標準的斗士。
N-COUNT
十字軍戰士
A Crusader was a knight who fought in the Crusades.
英漢詞典釋義
n.
<史>十字軍戰士
In a straight fight the crusaders usually won; in skirmishes, the Saracens often overcame their more numerous opponents.單打獨斗， 十字軍戰士通常會贏；在小規模戰斗中，撒拉遜人經常能以少勝多。
英英詞典釋義
Noun
1. a disputant who advocates reform
2. a warrior who engages in a holy war;
"the crusaders tried to recapture the Holy Land from the Muslims"