When was Mars Pathfinder first launched? 

December 4, 1996
Mars Pathfinder was launched December 4, 1996 and landed on Mars' Ares Vallis on July 4, 1997. It was designed as a technology demonstration of a new way to deliver an instrumented lander and the first-ever robotic rover to the surface of the red planet.
Mars Pathfinder was first launched on December 4, 1996. 