The major situational irony in Sophocles' Oedipus Rex revolves around the nature of legitimacy in rulership. When Oedipus arrives at Thebes, he has just solved the riddle of the Sphynx. In gratitude, the populace agrees to give him leadership of the city and he is betrothed to the Queeen. SInce, at this point, his rulership is on the basis of popular acclaim rather than birth, he is technically a "tyrant" not a king. When his parentage is discovered, he blinds himself and renounces his position as ruler. His parentage, of course, gives him legitimacy as a king, and thus the major situational irony is that Oedipus loses the rulership of Thebes just at the moment he is proved a legitimate hereditary ruler.