Arguably, the voice in Tennessee Williams's play A Streetcar Named Desire does not come from a character, but rather, it comes from the psyche of Blanche Dubois. It is not only because she is the main character, but because the entire plot is a consequence of, both, her actions, and her life experiences. For this reason, she does not directly voice the play, but her inner persona is what actually does it. This is why:
Regardless of the depth of the secondary characters, the strength of Blanche's feelings permeate the play, giving it an atmosphere of loss, nostalgia, and inevitability. After all, Blanche is the biggest loser here: She loses Belle Reeve, her reputation, her teaching license, her stability and, ultimately, her dignity and sanity. If you think about it, all these things happen as a result of ONE move from fate: Her once well-to-do Southern aristocratic family loses everything once her father dies. After that occurs, her fate seems to be sealed.
Therefore, Blanche's voice is heard throughout the play in her frustrations, in her strong desires, and her nature as a controversial woman. She is such a passionate person that it is impossible for her NOT to set a place at a hotel to meet "gentlemen callers". Equally, it is hard for her not to fall for one of her students, and then, equally, not to want to establish a relationship with Mitch once she gets to Stella's house. Blanche simply cannot help controversy. Even her behavior around Stanley causes the audience to worry about his reaction.
Hence, the voice in A Streetcar Named Desiredoes not necessarily come out of the mouth of a character, but out of the strength of a character's nature: Blanche's strengths and weaknesses are strong enough to dominate the entire style of narrative in the play.