Abraham Harold Maslow was an American psychologist. He is noted for his conceptualization of a "hierarchy of human needs", and is considered the father of humanistic psychology.
Maslow saw human beings' needs arranged like a ladder. The most basic needs, at the bottom, were physical -- air, water, food, sleep. Then came safety needs -- security, stability -- followed by psychological, or social needs -- for belonging, love, acceptance. At the top of it all were the self-actualizing needs -- the need to fulfill oneself, to become all that one is capable of becoming. Maslow felt that unfulfilled needs lower on the ladder would inhibit the person from climbing to the next step. Someone dying of thirst quickly forgets their thirst when they have no oxygen, as he pointed out. People who dealt in managing the higher needs were what he called self-actualizing people. Benedict and Wertheimer were Maslow's models of self-actualization, from which he generalized that, among other characteristics, self-actualizing people tend to focus on problems outside of themselves, have a clear sense of what is true and what is phony, are spontaneous and creative, and are not bound too strictly by social conventions.
Peak experiences are profound moments of love, understanding, happiness, or rapture, when a person feels more whole, alive, self-sufficient and yet a part of the world, more aware of truth, justice, harmony, goodness, and so on. Self-actualizing people have many such peak experiences.