I am a very big fan of Carl Jung, the founder of analytical psychology. I consider his process of individuation, breakdown of the mind into the fundamental cognitive functions, and theories about anima/animus and the collective unconscious to be very useful for self-development, getting along with a wide variety of people, and controlling (or not controlling) feelings.
MBTI & Fundamental Cognitive Functions
Learn about the Myers-Briggs Type Indicator, the world's most popular personality typology, based on Carl Jung's theory of the eight core mental processes that construct your reality and define the 16 personality types.
My MBTI personality type, likes & dislikes, interests, hobbies, aspirations, favourite actors, movies and shows - all this and way more than you could ever need to know about me.
For a couple years I have been conducting a personality adjustment experiment on myself based on MBTI theory which might be of some use to method actors, though the process may be irreversible, traumatic, immersive, expensive, and require a lot of sleep and hallucinogens with strong neurotrophic factors to physically rewire the brain. I believe it can fundamentally alter even an adult mind into having a specific, predictable personality, able to experience reality in surprising new ways but at the cost of reducing some previously had aptitude since strengthening one connection necessarily makes others relatively weaker. Interestingly, it may also cause them to possess a younger perspective since some of their mind would essentially be new. They would of course still retain their memories and previous values, though they may seem less vivid or important. The result of the experiment is I changed from an INTJ to an ENFP.