Great Scott! is an exclamation of surprise, amazement, or dismay.
Possible origins
The expression is of uncertain origin. It is believed to date back at least as far as the American Civil War, and may refer to the commander‑in‑chief of the U.S. Army, General Winfield Scott. The general, known to his troops as Old Fuss and Feathers, weighed 300 pounds (21 stone or 136 kg) in his later years and was too fat to ride a horse. A May 1861 edition of the New York Times carried the sentence:
:These gathering hosts of loyal freemen, under the command of the great SCOTT.
In an 1871...