I tried to translate "I don't care who he is" into Spanish, and I got this:
No me importa quién sea él
This sounds strange. sea is the present subjunctive (or imperative) conjugation of ser, which doesn't look right to me. I thought I should use es.
What is the difference, in this case, between indicative and subjunctive? Is it the same case about "dónde" (where) and "qué" (what)?
Let's say there's a knock on the door. You ask
¿Quién es?
Now let's say the phone rings, and you tell your brother, who's visiting and sitting next to the phone, not to answer it because you don't want to be interrupted, and you think it would be fine for whoever it is to leave a voicemail. You might say
No me importa quién sea. | I don't care who it is.
We use the subjunctive here, and it's kind of like saying "I don't care who it might be." (Here, we don't know who is calling, so there's uncertainty, which requires the subjunctive.)
Last scenario: Let's say the phone rings. You know it's your son calling for the umpteenth time that afternoon, but your brother doesn't know that, and wants to answer it, saying that it might be something important. You respond
Ya se quién es, y no me importa.
There's no uncertainty here, hence no subjunctive.
There are cases in which both indicative and subjunctive work, though with a subtle difference of meaning. In this specific case, in which identity is involved:
(1) ... quién sea él.
(2) ... quién es él.
one thing is clear: he does have an identity (a name, a role), which the speaker is not interested in discovering or in considering.
To understand the difference above, let's see a different pair of sentences:
We can thus see that the subjunctive casts some doubt as to the truth of the clause, while the indicative provides certainty.
If we apply this distinction to your pair of sentences, if the speaker uses (1) he wants to imply that he is not willing to believe that the other person is who he claims to be. If the speaker uses (2), he implies that he will not challenge his identity, hierarchy, authority, etc.
As a result, sentence (1) may be more pejorative: the speaker does not care who he is and, even if he finds out, he indicates that he is reluctant to believe it.
