Oscar Nelson (April 22, 1874 – April 2, 1951) was a Chicago City Alderman, one-time Auditor for the state of Illinois, and interim president of the Building Service Employees International Union, the precursor of the Service Employees International Union, in 1927. Nelson was born in Sweden. He emigrated to the United States and got a job as a delivery boy. He held employment as a grocery clerk, foundry worker and railway worker, but finally went into the banking industry and eventually became president of the Geneva State Bank and head of the Kane Co. Bankers' Association.