great Caesar's ghost

Allusion to the play The Tragedie of Iulius Cæsar by William Shakespeare, in which Roman leader Julius Caesar’s ghost appears to Brutus. Used as euphemism in place of good God or similar expressions. Made popular in the 1940s and 1950s by the Superman radio program and comic books as a catchphrase of the character Perry White.

The exclamation "Great Caesar's Ghost!" appears in the 1876 novel, The Adventures of Tom Sawyer by Mark Twain.