Eric Berne, the founder of Transactional Analysis developed the PAC model, the three ego states, Parent, Adult and Child. These are a mixture of behaviours, thoughts and feelings.

The Parent ego state, or exteropsyche - is a state in which people think and behave like their own parental figures did in their childhood. When in the Parent ego state people will often tell you "You are not allowed to do that", or "This is not good!". The Parent ego state can be Nurturing (supportive) or Critical.

The Adult ego state, or neopsyche - this is our internal computer. It is always rational, willing to find out more, analyzing everything, etc.

The Child ego state, or archaeopsyche - this is a state in which people behave, feel and think similarly to how they did in childhood.  Like the Parent ego state, the Child also has two sub divisions:  Adapted Child and Free Child. The Adapted Child will adapt to almost everything in order to get accepted. The Free Child is the one who is having fun, enjoying life, playing, telling jokes, etc.

Each of us are using all of these ego states. We are switching between them all the time but most of us love to use one of them especially.  For instance if your boss is telling you "You will stay here until you finish this project"  if you prefer the Adapted Child you will say "OK boss!".  If you like the Adult more you will reply "Why is it so important to finish it right now?". If you like the Parent more you will reply "You are not supposed to be so rude!". The Free Child would say "Yes boss", and after 5 minutes he is out with his friends doing something funny.