Freud hoped his model was universally valid and so turned to ancient mythology and ethnography for comparative material. Freud named his new theory the Oedipus complex after the famous Greek tragedy "Oedipus Rex" by Sophocles. "I found in myself a constant love for my mother, and jealousy of my father. I now consider this to be a universal event in childhood." Freud said. Freud sought to anchor this pattern of development in the dynamics of the mind. Each stage is a progression into adult sexual maturity, characterized by a strong ego and the ability to delay gratification (cf. "Three essays on the theory of Sexuality").