Simplify the following text for a Grade 12 native English-speaking person.
Original: Lee worked at Institute for Advanced Study and was a professor of physics at University of Pennsylvania , SUNY at Stony Brook , University of Chicago , and head of the theoretical physics department at Fermi National Accelerator Laboratory .
Simplified: Lee worked at Institute for Advanced Study . He was a professor of physics at University of Pennsylvania , SUNY at Stony Brook , University of Chicago , and head of the theoretical physics department at Fermi National Accelerator Laboratory .