Mr. 9

Mr. 9 is Princess Vivi's assigned male partner during her infiltration within Baroque Works. Not much is known about him other than he dressed like a prince and fights with acrobatics coupled with steel bats.

History
He and Vivi (known as Miss Wednesday at the time) meet the Straw Hats during the Laboon arc trying to kill the whale for food for their bounty hunting partners on Whisky Peak. The Straw Hats give them a ride there later after they accidentally lose their Log Pose (Grand Compass in English version).

After Vivi was exposed by Mr. 5 and Miss Valentine, Mr. 9 tried to hold them off to allow her to escape as he had grown fond of Vivi during their time together, declaring that they were still partners (effectively placing their loyalty to one another before loyalty to the company, an act frowned upon by Mr 5). Unfortunately, Mr. 5 (supposedly) kills him by hitting him with a Nose Fancy Cannon attack that exploded and knocked Mr. 9 into a river.

Trivia

 * In a recent character poll, Mr. 9 is currently ranked the 42nd most popular character in One Piece.