Charles Elachi is the director of NASA's Jet Propulsion Lab at Caltech. He leads JPL's efforts to build robots that explore space -- including the surprisingly long-lived Mars Rovers. In the wake of the Rovers' success (and even fame), it's worth remembering that they grew out of some troubled earlier attempts to reach Mars. Elachi's careful management of the Rover program, wrote the US News and World Report, was a key piece of its success. And Elachi gives equal credit to some extraordinary luck.
As JPL's director for space and Earth science programs from 1982 to 2000, and then its head since then, he's led the development of many new instruments and programs for observing Earth and exploring the planets. It's in part thanks to him that, as of May 2008, we have 17 different robots exploring space. His own academic specialty is active microwave remote sensing and electromagnetic theory.