Eldest of a literary trio

As a detective, I would first break down the clue into its key components: “eldest,” “literary,” and “trio.” I would immediately recognize the term “trio” as an indication that there are three things to look for. From there, I would consider classic literary trios, such as the three musketeers or the three witches from Macbeth. Given that this is a crossword clue, I would then think about the length of the answer and the patterns of the letters already filled in. A five-letter answer would be a good fit for “Athos,” one of the three musketeers. As “eldest” indicates the first-born or oldest of the trio in question, the answer is almost certainly Athos, who is described as the most mature and responsible of the musketeers. The detective in me would feel confident that Athos was the solution to the crossword puzzle, and I would be excited to fill in the answer and move on to the next clue.