Steve Nelson was an American agent of the Communist Party.
Nelson joined the party in 1925 when he was living in western Pennsylvania. When he moved to the bay area in 1942 he became chairman of the San Francisco branch of the Communist Party.
Almost immediately after taking that position, he became very involved in trying to uncover the work being done on the atomic bomb project at the University of California, Berkeley. He befriended many of the physicists working on the project with Communist leanings. In March of 1943 he met with one of them, Joseph Weinberg, who gave him information regarding the bomb. Nelson would eventually pass this information on to agents of the Soviet government.