For example, the audience learns through a letter or through someone else's conversation who this mysterious gentleman is and why he left the town many years before.

例如，观众通过一封信或其他人的谈话得知这位神秘的绅士是谁，以及他多年前为什么离开这个城市。

youdao

People wanted to know who this talented designer was.

人们想知道这位天才的设计者是谁。

《柯林斯英汉双解大词典》

We have no idea who this is.

我们不知道这个人是谁。

youdao

"It was like a giant jigsaw puzzle and the more we started to unearth and peel back the onion of who this guy was and what happened to him in the past and trying to truly understand the reason why he would be so obsessed with a specific case once we start to uncover these things about him we realized that once we explain one set of circumstances we needed to go even further with another set of circumstances."

VOA: standard.2010.02.27

This can be taken to extremes and the biggest extreme is the case of actors, which is if there's ever a case-- Anybody know who this is, the actor?

这个理论最极端的例子,就发生在演员身上，如果要举个例子…,大家知道这个演员是谁吗？

耶鲁公开课 - 心理学导论课程节选

So we have this anonymous attacker who dismisses Milton's earlier political treatises, especially The Reason of Church Government and other early works.

所以我们有这个匿名的抨击者,他否定了弥尔顿早期的政治论文，特别是《教会当局的原因》和其他早期作品。

耶鲁公开课 - 弥尔顿课程节选

And all of a sudden, it came so crystal clear to me who this guy was.

WHITEHOUSE: Remembering Senator Robert Byrd

But Grimoaldo doesn't really care who this newcomer is, and condemns him to death.

NPR: Riches Rediscovered:? Handel's 'Rodelinda'

But, as hard as he tried, he could not bring to mind who this stranger-unstranger was.

NEWYORKER: Heirs