These differences are to do with what the writer is assuming about the knowledge and attitude of the reader.
So, the writer thought that "being held captive by Robert Langton" would be likely to evoke in the reader's mind the question "Robert who?". To avoid that risk, the writer helpfully inserted the words "American professor" so that the reader can inwardly say "Oh, that Robert Langton". You will find many examples of this usage in journalism. I doubt that it is used much otherwise.
In the second case, the writer wants to save the reader the embarrassment of not knowing who Leo Tolstoy was. The definite article signifies that Tolstoy is an important person, so the reader who has never heard of him can think "OK this is about some famous guy. I ought to have known about him." This usage needs to be quite finely judged. It would be very odd to write for an English-speaking readership about "the English playwright William Shakespeare" because it would be assumed that he needs no introduction. Probably for a Russian-speaking readership you would not have to explain that Tolstoy was a writer.
The third example uses the definite article as a kind of title. "The Queen, The Leader, the megastar." That usage tells the reader that the writer thinks that the person referred to must be respected.