Although most sources agree that the expression "Great Scott" refers to an exclamation of surprise, wonder, shock or disbelief, sources do not agree on its origin. Several sources purport that its origin relates to a colorful General in the U.S. Army, Winfield Scott.
Scott, who joined the army in 1809 at the age of 23, was originally nicknamed Fuss and Feathers due to his preoccupation with uniform and procedure. He became a hero in both the War of 1812 and the Mexican War. It was during the Mexican War, however, that he was possibly re-named "Great Scott."
In 1846, President James Polk sent General Scott and his troops to fight with Mexico over the territory that is now New Mexico and California. Scott and his men won numerous battles and successfully occupied Mexico City in 1848. Although these facts are quite verifiable, the actual reason for the first utterance of "Great Scott" is, however, not so clear.
Some sources report that Scott was smug and boastful, such that the use of the expression "Great Scott" would actually be a form of sarcasm. We do know that following his army service, Scott campaigned as the Whig candidate for U.S. President in 1852. During this campaign, many jeered him as Great Scott. He lost the election by a narrow margin to the Democratic candidate Franklin Pierce,
Other possibilities on the origin of the phrase include that it is uttered similar a German greeting Gruess Gott, or Great God. Therefore, some feel the expression "Great Scott" is a euphemism for Great God. If this is the case, the phrase could be what is termed a minced oath, similar to how one might say darn in place of something more offensive.
No matter what its origin, the expression has taken on a life of its own. Those who have adopted Great Scott as a name include a TV series, a band, a store chain, a wrestler and at least one television cartoon character. The phrase itself is frequently used by comic book heroes, and actors in movies and television. Great Scott is uttered in the movie Back to the Future, in The Chronicles of Narnia series of books, and by Mr. Wilson, a character in the Dennis the Menace TV series.