Massive stars end their lives in spectacular explosions that drive shock waves into the surrounding medium. The early interaction is with mass lost before the explosion and analysis of the interaction gives clues on the nature of the exploding star. Most of the recently discovered superluminous supernovae may be cases with extreme mass loss. The later interaction with the interstellar medium can give rise to high energy gamma-ray emission through the acceleration of relativistic particles. Cases where dense matter is present are the most luminous. In addition to an outgoing shock wave, a massive star explosion can have an inner power source in the form of a pulsar (highly magnetized neutron star) with a relativistic, magnetized wind. Professor Chevalier is a leader in the field of high energy astrophysics, mainly supernovae. He won the Dannie Heineman Prize for Astrophysics. He is member of the US National Academy of Sciences.