* Søren Kierkegaard: While not a psychologist, Kierkegaard was a philosopher who explored themes of anxiety, despair, and the meaning of life – concepts that heavily influenced later existential psychologists.
* Jean-Paul Sartre: Another influential philosopher, Sartre's work on existentialism, particularly his ideas about freedom, responsibility, and authenticity, shaped the philosophical underpinnings of existential psychology.
* Martin Buber: Buber, a philosopher and theologian, emphasized the importance of dialogue and relationships in human existence, a concept that resonates with existential psychology's focus on the individual's experiences and interactions.
* Karl Jaspers: A psychiatrist and philosopher, Jaspers' work on the meaning of life, human freedom, and the limits of reason contributed to the development of existential thought.
* Viktor Frankl: A psychiatrist and Holocaust survivor, Frankl is considered a key figure in the development of existential psychology. He emphasized the search for meaning in life, particularly in the face of suffering.
* Rollo May: May was a prominent American psychologist who brought existentialist concepts to the field of psychotherapy. He focused on the anxieties, fears, and alienation experienced by individuals in modern society.
* Irvin Yalom: Yalom, a psychiatrist and author, continues to be a leading figure in existential psychotherapy. He has explored themes of death, freedom, and the search for meaning through his writings and clinical practice.
While these individuals contributed significantly to the development of existential psychology, it's important to note that the field is still evolving and drawing inspiration from various sources.