@krnel widely used in studies related to psychoanalysis and philosophy. According to psychoanalytic theory, the ego is part of the triad of the psychic model, formed by the ego, the superego and the ID.

The ego is considered as the "defender of the personality", since it is responsible for the prevention of the unconscious contents pass in the field of consciousness, thus triggering its defense mechanisms.
One of the main functions of the self is to harmonize the identification desires with the reality of the superego. So the ego suppresses the ID of unconscious desires to "fear" of punishments.
The ego is responsible for the differentiation that the individual is capable of performing, between their own internal processes and the reality that is presented to them.