He was a key figure in the campaign.

他是这场运动的关键人物。

Why is that a key figure?

为什么这个数字非常关键？

The guy is a key figure in the investigation.

那家伙是这次调查工作的关键 要害人物。

Wu Yong is a key figure in a famous classical lifurature book named" water land".

吴用是《水浒传》中的线索式人物，是众人物的灵魂。

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’。