PhysicsWeb has published an article on the greatest mathematical physicist you've never heard of, James Maxwell.
Physicists may be familiar with Maxwell, but most non-scientists, when they switch on their colour TVs or use their mobile phones, are unlikely to realize that he made such technology possible. After all, in 1864 he gave us "Maxwell's equations" – voted by Physics World readers as their favourite equations of all time – from which radio waves were predicted.
...Or consider relativity: mention it and everyone thinks of Einstein. Yet it was Maxwell in 1877 who introduced the term into physics, and had noticed well before then how the interpretation of electromagnetic induction was different depending on whether one considers a magnet approaching a wire loop or a loop approaching a magnet. It was from these 'asymmetries that do not appear to be inherent in the phenomena' that Einstein began his work on special relativity
...Even if his achievements are somewhat overshadowed in the public's eye by those of Einstein, whose successes were marked by a great series of events last year, it is a measure of Maxwell's standing that 2006 – the 175th anniversary of this birth – has been dubbed Maxwell Year.
Wikipedia: Maxwell's equatations