MacMillan, Donald Baxter (1874-1970), a United States Arctic explorer and scientist. Between 1908 and 1958 he made more than 30 expeditions to the Far North, pioneering in the use of the airplane and short-wave radio. He made valuable contributions to Arctic geography, geology, botany, and zoology, and to the understanding of Eskimo culture.

MacMillan joined Robert Peary's polar expedition of 1908-09, which succeeded in reaching the North Pole for the first time. MacMillan himself did not reach the pole, however. During 1910-12 he made ethnological studies of Labrador Eskimos and Indians. MacMillan led his first expedition during 1913-17. He surveyed the Greenland ice cap and he proved that Crocker Land, an area that Peary thought he had sighted west of Ellesmere Island, did not exist. On the 1925 expedition, Richard Byrd, MacMillan's assistant, made the first successful effort to explore the Arctic by airplane. Botanists of the 1938 expedition returned with 40,000 plant specimens.

MacMillan was born in Provincetown, Massachusetts, and graduated from Bowdoin College in 1898. He served in the aviation branch of the U.S. Naval Reserve during World War I. He was recalled to active duty in 1941, and during World War II commanded aerial photography squadrons on flights over the Arctic. He retired from the reserve in 1954 with the rank of rear admiral.