I wonder if he is the brother of mega-moron Michael Eric Dyson (or is it Eric Michael, I forget)?
Freeman Dyson is the co-developer of Quantum Electrodynamics in the late 1940s (along with Richard Feynman, Julian Schwinger, and Shinichiro Tomonaga). The other three were awarded the Nobel Prize for the work, but only three people can share the same prize. He also worked on the Orion project in the 50s and early 60s to develop a nuclear rocket.
He is the father of Esther Dyson, the technology writer, and George Dyson, a somewhat less well-known science writer.