Great Scott

An exclamation of surprise or incredulity and is almost certainly American from the mid-19th century but soon anglicised and in wide use by the end of that century. Its origin is a matter of considerable debate. But no one knows for sure whether the Scott in question alludes to a real person named Scott (and there are several candidates including an American general named Scott and Sir Walter Scott) or is simply a minced oath for God. The origin, therefore, remains obscure.