Yoichiro Nambu
Kleppa retired as a Professor Emeritus in 1990, but he maintained his lab and continued to receive grants until his death. He held on to his Norwegian citizenship until 2000, when he became a U.S. citizen. He was a friend and colleague of R. Stephen Berry, Stuart Rice, Robert Gomer, Thomas Rosenbaum, and Nobel Laureates Yoichiro Nambu and Subrahmanyan Chandrasekhar.