He was a key figure in the campaign.

他是这场运动的关键人物。

《牛津词典》

Why is that a key figure?

为什么这个数字非常关键？

youdao

When I was working with Graham, a key figure in the Python team, I thought 'This is the Big Break.'

当我跟Python团队一个关键成员Graham一起工作的时候，我想‘这真是个大突破’。

youdao

Homeland Security Secretary Janet Napolitano, a key figure behind this week's aid package, will visit Mexico early next month along with U.S.

VOA: standard.2009.03.25

Republican political strategist Terry Nelson agrees that Pelosi was the key to passing health care reform, but points out that she is a polarizing figure for many conservatives.

VOA: standard.2010.05.11

At the time, officials described him as a key figure in the Sinaloa cartel.

BBC: Mexico arrests Joaquin 'El Chapo' Guzman's father-in-law

And who is the biggest car dealer of them all and a key figure in Avtovaz?

FORBES: Godfather of the Kremlin?

Sistani has been a key figure since the U.S.-led invasion of Iraq in 2003.

NPR: Sectarian Violence Erodes Sistani's Influence in Iraq