Donald Wills Douglas Sr. (April 6, 1892 – February 1, 1981) was an American aircraft industrialist and engineer. 

An aviation pioneer, he designed and built the Douglas Cloudster. Though it failed in its intended purpose—being the first to fly non-stop across the United States—it became the first airplane with a payload greater than its own weight.

He founded the Douglas Aircraft Company in 1921 (the company later merged with McDonnell Aircraft to form McDonnell Douglas Corporation). Under his leadership, the company became one of the leaders of the commercial aircraft industry, engaging in a decades-long struggle for supremacy with arch-rival William Boeing and the company he founded, Boeing. Douglas gained the upper hand, particularly with his revolutionary and highly successful Douglas DC-3 airliner and its equally popular World War II military transport version, the C-47; at the start of the war, his airplanes made up 80% of all commercial aircraft in service. However, he lagged behind in the jet age and was overtaken and surpassed by Boeing. He retired in 1957. 

Douglas was born in Brooklyn, New York, the second son of an assistant cashier at the National Park Bank.
He attended Trinity Chapel School and was of Scottish descent.

After graduation in 1909, he enrolled in the Naval Academy in Annapolis, Maryland. He had been an early aviation enthusiast; at the age of 16 in the fall of 1908, he convinced his mother that he needed to witness the Fort Myer trials of the Wright Flyer. He later built model airplanes, some with rubber-bands and other motors, in his dormitory room at Annapolis and tested them on the grounds and in the academy's armory. In 1912 he resigned from the academy in order to pursue a career in aeronautical engineering.