What is the origin of the saying “Great Scott!”? Who is Scott and why is he great?
General Winfield Scott
From this site.
As the cite above indicates later, the German phrase “Gruss Gott” is the most likely explanation.
Attributions to particular persons such as General Scott are more likely to be adaptations of a known phrase. I have heard it applied to Scott the polar explorer too, although the phrase pre-dates him.