Which among these sentences is right?

[gseran]

Which among these sentences is/are correct?

1. What defines him are the traits he displays.
2. What defines him is the traits he displays.
3. What define him are the traits he displays.

[Raymott]

Which among these sentences is/are correct?

1. What defines him are the traits he displays.
2. What defines him is the traits he displays.
3. What define him are the traits he displays.

1. sounds the most natural to me. But I'm not saying it's the only correct version.

The problem with sentences like this is that "What" can take a singular copular verb (is) even if the predicate is plural.
4. "What he lives for is his children." sounds better than "What he lives for are his children."
But we (I?) would say, "His children are what he lives for."

[gseran]

Thank you. I thought so too. I was hoping that there would be just one right answer for sure. Guess I'll just have to frame the sentence differently to avoid the doubt.

[jegan0825]

NOT A TEACHER!
I too would go with option 1
It seems the most appropriate option to me.

[jegan0825]

NOT A TEACHER!

1. sounds the most natural to me. But I'm not saying it's the only correct version.

The problem with sentences like this is that "What" can take a singular copular verb (is) even if the predicate is plural.
4. "What he lives for is his children." sounds better than "What he lives for are his children."
But we (I?) would say, "His children are what he lives for."

Actually when you say "What he lives is his children.", the "is" is related him and not the children. The reason for him to live is singular. He has, genreically, a commitment.
When you say "His children are what he lives for", having children becomes a cause, and naturally it is in the plural form.

This is what I understood. Am I correct?

[5jj]

Actually when you say "What he lives for is his children.", the "is" is related to him and not the children.

No. We could also say, "What they live for is their children". 'What he lives/they live for' is the subject of the verb 'is'.