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.他自认是一位追求更高的新闻和广播标准的斗士。
N-COUNT
十字军战士
A Crusader was a knight who fought in the Crusades.
英汉词典释义
n.
<史>十字军战士
In a straight fight the crusaders usually won; in skirmishes, the Saracens often overcame their more numerous opponents.单打独斗, 十字军战士通常会赢;在小规模战斗中,撒拉逊人经常能以少胜多。
英英词典释义
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"