Learn Swedish: Vem är det som kan gestalta karaktären bäst? - Who is it that can portray the character best?

Both are grammatically correct, but Vem är det som (Who is it that) is a cleft sentence used for emphasis. By splitting the sentence into two parts, it places a much stronger focus on the identity of the person. It often implies a process of elimination, like trying to pick the absolute best candidate out of a specific group of actors.

Is the word som strictly necessary in this sentence?

Yes, it is absolutely mandatory here. In these cleft constructions, som acts as the subject of the relative clause (som kan gestalta...). In Swedish, you can sometimes drop som if it is the object of the clause, but you can never drop it when it is the subject.

What is the difference between using gestalta and just using spela (to play) here?

Gestalta means to portray, give shape to, or depict (it comes from the noun gestalt, meaning figure or shape). While spela en karaktär simply means to play a character, gestalta carries a deeper, more artistic nuance of truly bringing the character's inner life and personality to the stage or screen.

Can karaktär mean a fictional character in Swedish, or is it a false friend?