stolen from
LileksWho the heck is Scott anyway? And why is his name being used as an ejaculation of surprise?
According to
World Wide Words, it comes from either German immigrants in America using their traditional ejaculation "Grüß Gott!" (the little
ß character isn't a funky B; it's a German letter standing for a double S - thus leading to something kinda sort like "Groo-Scott") or it's a reference to Winfield Scott, the hero of the Mexican-US War, since the phrase first pops up in the 1860s at the height of Scott's fame (he was the commanding general of the army at the start of the Civil War, but was too old to take the field, so his reputation never suffered).
Personally, I have never used this ejaculation. Superman ejaculated "Great Scott" quite frequently in cartoons when I was a kid, so the ejaculant took on a certain corny flavor. The British seemed to take in this ejaculation as their own--it shows up in the Chronicles of Narnia, Sherlock Holmes movies, and most recently it has splashed into Harry Potter books.