Har-rumpf and egad, it’s Major Hoople
Great Caesar’s ghost! Now there’s an expression you most likely haven’t heard in a long time, if ever.
Nonetheless, it was once common, especially here in the Midwest. Most likely the expression was first used sometime in the late 19th century. Along with “great Scott,” “great Caesar’s ghost” was a substitute for the once commonly used “great God.”
It is not exactly clear why “great God” fell out of favor. The best explanation seems to be that the more prim and proper elements of society felt it was dangerously close to violating the 4th Commandment.