Great Caesar's Ghost, or simply Caesar (possibly Caius Julius Caesar) is one of the ghosts haunting the Haunted Mansion.
On one end of the Grand Hall's Birthday Party table, the ghost of an old man wearing a laurel crown and a toga sits in an elaborate chair, smiling contentedly while across from the Birthday Ghost. This character is identified as the ghost of Caesar and is a play on the then-current expression "Great Caesar's Ghost!", hence his name.
"Great Caesar" can refer to any of the numerous Roman leaders who succeeded to the first famous Caesar, Gaius Julius Caesar; it could notably be Emperor Augustus Caesar. However, Julius Caesar was nicknamed "the Bald" in his time due to thinning hair, and the Mansion's Great Caesar's Ghost is bald, suggesting he is probably meant to be Julius.
Along with this the expression "Great Caesar's Ghost" is an allusion to the play Julius Caesar by William Shakespeare where Gaius's friend-turned-murderer Brutus starts having visions of the senator haunting him.
In history, Gaius Julius Caesar (first name Gaius, last name Julius, "cognomen" or "hereditary nickname" Caesar) was a strategically brilliant Roman senator and military leader who launched several illegal conquests out of Italy without the permission of the Roman Republic. However, Julius's conquests were incredibly prosperous, greatly expanded the Roman Empire and created the extremely efficient Thirteenth Legion. The Republic however saw this as Caesar's attempt at making himself "King of Rome" and after several squabbles, settled on having him assassinated by stabbing him within the Republic building with 23 times. Following his death, the Roman people became outraged and demanded an Emperor who would replace the Republic which killed their beloved Caesar so Gaius's nephew Octavian was appointed Emperor of Rome.
- Great Caesar's Ghost was first mentioned by Ken Anderson among various historical and famous ghosts he planned to have in the Mansion. He is one of the very few of these characters that Marc Davis retained when he took over the project.
- In the Marc Davis concept art, the character is somewhat plump; meanwhile, the actual animatronic used in the end is very skinny, bordering on skeletal.
- At one point it was also planned for the ghost of the Roman emperor Nero to be found in the Tokyo Haunted Mansion which would have meant Caesar wouldn't have been the only ghost of a Roman leader in the Mansion. Along with this the male Chandelier Ghost resembles a Roman soldier and can be interpreted as a representation of Mark Antony, Caesar's general and close-friend in life.
- The character has sometimes been thought to be Martin, a character on a tombstone described as an "Old Spartan", by people who weren't aware of the "Cæsar" connection. Regardless of it, Martin is, anyway, not supposed to be an ancient Spartan, but more likely an inhabitant of any of the dozens of towns named Sparta in the United States of America, or even simply someone called "Spartan" because of his stern habits.
- In the video game, Caesar mocks the "ides of March", stating that he has nothing to fear, a reference to the Shakespeare play Julius Caesar.