I promise not to get too academic, but we have to think, perhaps, of the distinction that has obsessed modern thought, between signifiers and signified, about subjectivity and identity, about representation, about difference, about the slipperiness of meaning as regards the word. Just the voice. One man's voice. While we sometimes feel that a monologue is a private musing we overhear, it can also be something shared, wherein we become complicit, especially in the form of a monodrama. There is also the notion that the character delivering the dramatic monologue is a bit like the Ancient Mariner, someone who's buttonholed you.
Every narrator creates voices.
Aristotle and Plato identified three basic kinds of narration - the narrator's own voice, the assumed voice of someone else and a mixture of their own voice and others. The question we avoid is which of these voices we are hearing. Richard Burton was, of course, a real person, though no longer able to prevent Mark Jenkins from putting words into his mouth. Jenkins offers us his version of the actor Richard Burton and has given him words to say which, the author might presumably argue, explore with creative freedom Burton's perceived personality. Ted is a truly fictional character, a man who is seen to have such a distorted view of reality that it makes him behave in an abnormal way.