U.S. President Barack Obama has formally nominated Sung Kim, a career diplomat with expertise in Korean affairs, as his new ambassador to Seoul, the White House announced Friday. If his nomination is confirmed by the Senate, Kim, 51, will replace Kathleen Stephens and become the first person of Korean origin to serve as U.S. ambassador to Seoul. Kim immigrated to the U.S. in the 1970s and obtained U.S. citizenship in 1980.