Great Caesar's Ghost!
From superman.nu: Supermanica
Great Caesar's Ghost!
A guise that Daily Planet reporter Waldo Pippin uses in order to get over his fear of Perry White and get better stories as part of an elaborate hoax devised with the help of Superman.
"I realized that I couldn't do my best work while I was scared of you so Superman suggested that I enact the ghost. And once I saw you scared of me I lost my fright and was able to do better stories" (S No. 91/3, Jun 1954: "Great Caesar's Ghost!").
"Great Caesar's Ghost!" is also a trademark exclamation of Daily Planet editor Perry White.