geu jawonbongsajaneun daedanhapnida.

Here, 그 means that and modifies 자원봉사자, so 그 자원봉사자 means that volunteer.

Korean 그 can sometimes refer to he in certain contexts, but not in this sentence. Because it comes directly before a noun, it is working as a determiner: that.

자원봉사자 means volunteer.

It can be understood as:

• 자원봉사 = volunteer work / volunteering
• 자 = person

So the full word literally means a person who does volunteer work.

는 is the topic marker.

So 자원봉사자는 means something like as for the volunteer or the volunteer, .... In natural English, we usually do not translate this directly. It just helps organize the sentence in Korean.

In this sentence, 는 tells us that that volunteer is the topic being talked about.

Yes, you could say 그 자원봉사자가 대단합니다, but the nuance changes a little.

• 은/는 marks the topic and can sound more like you are making a general comment about that volunteer.
• 이/가 marks the subject more directly and can sound more focused, as if identifying who is impressive.

So:

• 그 자원봉사자는 대단합니다 = That volunteer is impressive / speaking about that volunteer
• 그 자원봉사자가 대단합니다 = That volunteer is the impressive one / more subject focus

대단합니다 comes from the dictionary form 대단하다.

It is usually translated as an adjective in English, such as:

• great
• amazing
• impressive
• remarkable

But in Korean grammar, words like this behave more like descriptive verbs, so they can end a sentence by themselves.

There is no separate word for is here.

English says That volunteer is amazing. Korean expresses is amazing all together in 대단합니다.

So the sentence structure is basically:

• 그 자원봉사자는 = that volunteer
• 대단합니다 = is impressive / is amazing

The ending -ㅂ니다 / -습니다 is a formal polite ending.

So 대단합니다 is a formal, polite way to say is amazing.

Compare:

• 대단합니다 = formal polite
• 대단해요 = polite, less formal
• 대단하다 = dictionary form / plain form

You might hear -ㅂ니다 in speeches, presentations, news, announcements, or respectful public situations.

It is usually stronger than just good.

대단하다 suggests that someone or something is:

• impressive
• remarkable
• admirable
• amazing

So 그 자원봉사자는 대단합니다 does not just mean the volunteer is nice or decent. It suggests real admiration.

Korean usually puts the main predicate at the end of the sentence.

English:

• That volunteer is amazing

Korean:

• That volunteer + topic marker + amazing-is

So 대단합니다 comes last because Korean normally saves the main descriptive or verbal part for the end.

Not exactly.

그 usually means that, not just the.

Korean does not have articles that match English a/an/the exactly. Very often, Korean leaves that idea to context. But when 그 is used before a noun, it usually points to something specific, like that volunteer.

It is commonly pronounced closer to 대단함니다 than 대단합-nida.

This happens because in 합니다, the ㅂ sound changes before ㄴ, so it sounds like ㅁ.

So a natural pronunciation is close to:

dae-dan-ham-ni-da

Yes, it is completely natural.

It sounds like a polite, respectful statement such as:

• praising a volunteer in conversation
• making a comment in a formal setting
• speaking respectfully about someone’s actions or character

If you wanted a less formal everyday version, you could say:

그 자원봉사자는 대단해요