Sigmund Freud

Perhaps Freud's single most enduring and important idea was that the human psyche (personality) has more than one aspect. Freud's personality theory (1923) saw the psyche structured into three parts (i.e., tripartite), the id, ego and superego, all developing at different stages in our lives. These are systems, not parts of the brain, or in any way physical. According to Freud's model of the psyche, the id is the primitive and instinctual part of the mind that contains sexual and aggressive drives and hidden memories, the super-ego operates as a moral conscience, and the ego is the realistic part that mediates between the desires of the id and the super-ego.
Although each part of the personality comprises unique features, they interact to form a whole, and each part makes a relative contribution to an individual's behaviour.


The id is the primitive and instinctive component of personality. It consists of all the inherited (i.e., biological) components of personality present at birth, including the sex (life) instinct – Eros (which contains the libido), and the aggressive (death) instinct - Thanatos.
The id is the impulsive (and unconscious) part of our psyche which responds directly and immediately to the instincts. The personality of the newborn child is all id and only later does it develop an ego and super-ego.
The id remains infantile in its function throughout a persons life and does not change with time or experience, as it is not in touch with the external world. The id is not affected by reality, logic or the everyday world, as it operates within the unconscious part of the mind.
The id operates on the pleasure principle (Freud, 1920) which is the idea that every wishful impulse should be satisfied immediately, regardless of the consequences. When the id achieves its demands, we experience pleasure when it is denied we experience ‘unpleasure’ or tension.
The ego develops to mediate between the unrealistic id and the external real world. It is the decision-making component of personality. Ideally, the ego works by reason, whereas the id is chaotic and unreasonable.


The ego operates according to the reality principle, working out realistic ways of satisfying the id’s demands, often compromising or postponing satisfaction to avoid negative consequences of society. The ego considers social realities and norms, etiquette and rules in deciding how to behave.
Like the id, the ego seeks pleasure (i.e., tension reduction) and avoids pain, but unlike the id, the ego is concerned with devising a realistic strategy to obtain pleasure. The ego has no concept of right or wrong; something is good simply if it achieves its end of satisfying without causing harm to itself or the id.
Often the ego is weak relative to the headstrong id, and the best the ego can do is stay on, pointing the id in the right direction and claiming some credit at the end as if the action were its own.
The superego incorporates the values and morals of society which are learned from one's parents and others. It develops around the age of 3 – 5 during the phallic stage of psychosexual development.


The superego's function is to control the id's impulses, especially those which society forbids, such as sex and aggression. It also has the function of persuading the ego to turn to moralistic goals rather than simply realistic ones and to strive for perfection.


The superego consists of two systems: The conscience and the ideal self. The conscience can punish the ego through causing feelings of guilt. For example, if the ego gives in to the id's demands, the superego may make the person feel bad through guilt. The ideal self (or ego-ideal) is an imaginary picture of how you ought to be, and represents career aspirations, how to treat other people, and how to behave as a member of society. Behaviour which falls short of the ideal self may be punished by the superego through guilt. The super-ego can also reward us through the ideal self when we behave ‘properly’ by making us feel proud.


If a person’s ideal self is too high a standard, then whatever the person does will represent failure. The ideal self and conscience are largely determined in childhood from parental values and how you were brought up.

Sources:
https://www.simplypsychology.org/psyche.html
Freud, S. (1920). Beyond the pleasure principle. SE, 18: 1-64.
Freud, S. (1923). The ego and the id. SE, 19: 1-66.