It’s at the end of “Oedipus”

The answer to the crossword question “It’s at the end of ‘Oedipus'” is SIGMA. The reason for this is that Sigma is the 18th and final letter in the Greek alphabet. The play “Oedipus Rex” by ancient Greek playwright Sophocles is written in Greek and would have originally ended with the letter Sigma. This crossword question is likely testing the player’s knowledge of the Greek alphabet or their familiarity with “Oedipus Rex” and its original language.