Carl Rogers (1902 - 1987) was one of the most influential psychologists of modern times, and is well known for the creation of Client-Centered Therapy, also known as Person-Centered Therapy or Rogerian Psychotherapy. As the name implies, this method of therapy emphasizes the person as the subject, rather than an object. The client-therapist relationship is not one where the therapist's role is to cure or change the person. Rather, the therapist's role is to create a positive relationship that the client may use as a means of personal growth.
Rogers believed that humans have a "Self-Actualizing" tendency - an innate drive that pushes the person to fulfill his potentials. A "Fully-Functioning Person" is an individual who is continually moving toward self-actualization. This type of person is open to life's experiences, has trust in himself, and is able to express his feelings and act independently.
However, to become a fully-functioning person, one needs to have experienced Unconditional Positive Regard and not have developed "Conditions of Worth." Oftentimes as children, we receive positive regard from significant people, notably our parents, only when we meet certain conditions. For example, a child may feel that he is loved when he's told that he is being a "good boy" but not when he has misbehaved. This creates conditions of worth, where the child feels that he becomes worthy of love only when his actions are consistent with what is expected of him.
Rogers believed that the work of the therapist is to create a relationship with the client where he is able to experience Unconditional Positive Regard so that he may be able to grow and become a fully-functioning person.