Final answer:
Dwight D. Eisenhower was the Supreme Allied Commander in the European theater of war during World War II, leading the Allied forces to victory against the Axis powers.
Step-by-step explanation:
The role of the Supreme Allied Commander in the European theater of World War II was a critical position held by Dwight D. Eisenhower. Under his leadership, a vast army was mobilized to face the Axis powers in Europe. Eisenhower was instrumental in planning and executing major campaigns, including the D-Day landings in Normandy.
He was a five-star general who, after his military service, went on to become President of the United States. While George C. Marshall was key in expanding the U.S. Army and served as Army Chief of Staff, Admiral Chester Nimitz commanded the US Pacific fleet, and General Douglas MacArthur was in charge of the Southwest Pacific Area, it was Eisenhower who served as the commanding general of the European theater of operations.
Therefore, the answer to the question about the Supreme Allied Commander in the European theater of war is option 2) Dwight Eisenhower.