How did Oedipus become the King of Thebes?

Oedipus became the King of Thebes by answering the riddle of the Sphinx. The Sphinx, a creature with the body of a lion and the head of a human, was terrorizing Thebes by posing a riddle to anyone who wished to enter the city. Those who could not solve the riddle were killed. Oedipus encountered the Sphinx on his journey to Thebes, and by correctly answering her riddle—"What walks on four legs in the morning, two legs at noon, and three legs in the evening?"—he not only liberated the city from the Sphinx's curse but also won the throne as a reward for his cleverness and bravery. This act established his role as a hero and leader among the citizens of Thebes.

Winning a battle, inheriting the throne from his father, or marrying the queen are not the correct pathways described in the play for Oedipus's rise to power. His ascent to kingship is primarily tied to his intellectual victory over the Sphinx, marking him as a figure of both fate and free will.