Basilis C. Xanthopoulos (also Vasilis; Greek: Βασίλης Κ. Ξανθόπουλος; 1951 – 27 November 1990) was a Greek theoretical physicist, well known in the field of general relativity for his contributions to the study of colliding plane waves.
Basilis Xanthopoulos was born in Drama, in 1951. After majoring in mathematics at the University of Thessaloniki he moved to the University of Chicago, where he earned his Ph.D. in 1978. During this time, he collaborated with Subrahmanyan Chandrasekhar on colliding plane waves. In particular, they discovered an exact solution which models two gravitational plane waves which collide, interact nonlinearly, and create in the interaction zone a curved region of spacetime which is locally isometric to the Kerr vacuum. This is now called the 'Chandrasekhar–Xanthopoulos colliding plane wave model.'
Xanthopoulos and his colleague Stephanos Pnevmatikos were murdered by a 32-year-old disgruntled post-graduate student, named Giorgos Petrodaskalakis (who later committed suicide), on the evening of 27 November 1990 at the University of Crete.