Step 1: Identifying the thinkers of Existentialism.
- Jean-Paul Sartre and Albert Camus are central figures in the existentialist movement, exploring themes such as freedom, choice, and the absurd.
- Søren Kierkegaard is considered a precursor to existentialism, as he addressed themes of individual choice and responsibility.
- Roland Barthes, however, is a structuralist and post-structuralist thinker, primarily known for his work in semiotics, literature, and cultural theory, rather than existentialism.
Step 2: Conclusion.
Therefore, the correct answer is (C), as Roland Barthes does not belong to the existentialist tradition.