Devil Fruit: Gasu Gasu no Mi

Caesar Clown, also referred to as "Master" by his underlings, is a former colleague of Vegapunk and the main antagonist of the Punk Hazard Arc. Caesar is the leading expert on mass-murder weapons and is a mad scientist with a bounty of 300,000,000 beli on his head.

He appears to have a grudge against Vegapunk, as well as a somewhat rational personality, as shown when he hid from the Marines instead of trying to fight them immediately, as well as trusting Monet's deduction that the Straw Hats might be more powerful than their bounties claim and waiting for Joker's approval to make his actions look like accidents, before starting attacks. Caesar is also a rather economizing person, as he didn't want to waste the poison, by clearing it off but rather collected, saved and compressed it into Smiley. It was stated by Smoker that he was one "crazy bastard".

He is a very prideful person, going as far to say that his work four years ago on the mass murdering weapon that caused the Punk Hazard incident was not a failure, but instead was a great success, hinting at a superiority complex. Unlike most Logia users, Caesar keeps his Devil Fruit power activated all the time and is either completely or partly turned into gas.

He also demonstrates tendencies of a superiority complex when Luffy mentioned his Gasu Gasu no Mi had no effect on his immune system due to Magellan's Doku Doku no Mi, both being poisonous Devil Fruits of differentiating class, and Caesar became rapidly aggravated in the fact of Luffy comparing his Logia powers to that of a "mere" paramecia user.

He is very ruthless, as he used the blind trust of his injured subordinates to test a newly developed gas and told the Yeti Cool Brothers to kill Brownbeard when he thought he was no use to him anymore. He also used the restricted drug NHC10 to maintain his hold on the children he kidnapped, knowing that they will be unable to escape due to the painful withdrawal symptoms; Law found this aspect of Caesar disgusting. Caesar also seems to like cocktails, as he is often seen holding a cocktail glass.

He has a distinct laugh of "Shurororororo".