You can describe a person or thing that causes a change or event to happen as a catalyst .
例句
I very much hope that this case will prove to be a catalyst for change...我非常希望這起事件能催生變革。He said he saw the bank's role as a catalyst to encourage foreign direct investment.他說，他認為銀行就應該起到刺激外國直接投資的作用。
N-COUNT
(化學)催化劑
In chemistry, a catalyst is a substance that causes a chemical reaction to take place more quickly.
英漢詞典釋義
n.
<化>催化劑,觸媒
A catalyst is a substance which speeds up a chemical reaction.催化劑是一種能加速化學反應的物質。It acts as a catalyst in the process of fermentation.它在發酵過程中起觸媒的作用。
促進因素;有感染力的人,能激發對方的人
The workers’ demand for better conditions was a catalyst for social change.工人們要求改善工作條件促進了社會變革。
英英詞典釋義
Noun
1. (chemistry) a substance that initiates or accelerates a chemical reaction without itself being affected
2. something that causes an important event to happen;
"the invasion acted as a catalyst to unite the country"