Gustaf Wilhelm Hammar (Gustav Vilhelm Hammar) (June 22, 1893 – August 19, 1954) was a Swedish-born American experimental physicist. He was the eldest of six children of Anders Vilhelm Hammar and Elin Christina Hammar (née Olsson). He emigrated to the United States in 1913, attended Bethel University in St. Paul, Minnesota, and by 1920 was married and living with his wife, Louise (with whom he was ultimately to have four children), in King County, Washington.