Carl Rogers, from USA, was a therapist who was very influential in the development of Person Centred Therapy (which I will refer to as PCT just for convenience) in the 1940’s and 1950’s.
Such was his influence that it is sometimes referred to as Rogerian Therapy. One of the most influential and widely read books about PCT is entitled On Becoming a Person by Carl Rogers. It is well worth reading to get a good overview of this form of healing. It is a relatively jargon-free book, and is full of common sense.
The new and radical (at that time) ideas of Rogers were influenced by thinking promoted by philosophers such as Jean-Paul Sartre, Martin Buber, Paul Tillich and others.
Such philosophers explored many and varied aspects of being human, but from our point of view the most important thing to note was that they focused on human relationship as being fundamental to our existence.
The principles and general methods of Person Centred Therapy, which focused on personal power and healing from within rather than being cured by an external expert, took a long time to be accepted in the therapeutic world as psychology in the USA was at that time dominated by psychiatry and behaviourism which I have described already.