Sigmund Freud, an Austrian neurologist, created psychoanalysis and founded clinical psychiatry as we know it today. His theories have been challenged and changed but remain the base of modern psychiatry.
Erik Erikson, of Danish descent but raised in Germany, was a student of psychoanalysis and an influential figure in post-Freudian psychiatry.
While Freud focused on the unconscious mind and psychosexual development, Erikson focused on stages of life as a whole. Freud's basic theory is that all activity in life is based in our unconscious desires as created in infancy by our latent sexual needs; the Ego is subservient to the Id. In contrast, Erikson theorized that the Ego, in its ability to consciously understand and accept the Id, has the power to supercede it without falling prey to mental damage.
In addition, Erikson claimed that personal development didn't stop with Freud's Genital stage, extending to death; instead, each of Erikson's eight stages of life is marked by a conflict -- for example, a teenager is rooted in Identity vs. Role Confusion: the classic "Who Am I?" These stages cover the entirety of life and postulates that humans have the ability to overcome each conflict in turn, understanding and accepting the extremes of each, resulting in a rounded individual. He also concluded that personality is a product of environment, instead of Freud's theory that everyone has similar unconscious desires which manifest in different ways regardless of environment.
Erikson's emphasis, therefore, is on the Ego conquering the Id; man's ability to reason gives him the power to comprehend his innate desires and control them, instead of letting them control him.