Melanie Klein was an Austrian-British author and psychoanalyst known for her work in child analysis. She was the primary figure in the development of object relations theory. Klein suggested that pre-verbal existential anxiety in infancy catalyzed the formation of the unconscious, which resulted in the unconscious splitting of the world into good and bad idealizations. In her theory, how the child resolves that split depends on the constitution of the child and the character of nurturing the child experiences. The quality of resolution can inform the presence, absence, and/or type of distresses a person experiences later in life.

Karl Abraham was an influential German psychoanalyst, and a collaborator of Sigmund Freud, who called him his 'best pupil'.