Vegapunk

Dr. Vegapunk is the leading scientist of the SSG and in the employment of the Marines. His work includes discovering the secrets and uses of seastone, the secrets of how Devil Fruit powers work, the co-discovery of the Lineage Factor and its applications, the creation of the Pacifista and Seraphim, and various other scientific achievements that are said to be at least 500 years ahead of current technology. He hails from the technologically advanced Karakuri Island and currently resides on Egghead, where his laboratory is located. Before being employed under the World Government, Vegapunk had been the director of an outlaw scientific research team known as MADS, where he worked alongside other notable scientists such as Caesar Clown, Vinsmoke Judge, Queen, and Buckingham Stussy. The team was eventually arrested, and Vegapunk was later integrated into the Marines as its head scientist after MADS' dissolution. This was until Vegapunk became enemies with the World Government once more, when the World Government dispatched CP0 in attempt to kill him. He and his satellites are major allies to the Straw Hats during the Egghead Arc.

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When one of his satellites, York, betrays him by revealing to the World Government that Vegapunk was researcing the Void Century, they dispatched CP0 and conspired with her to eliminate him, which resulted in the monumental Egghead Incident.

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Vegapunk was killed by his old friend, Admiral Kizaru, during the ensuing Buster Call on Egghead. Foreseeing his assassination, however, Vegapunk left behind an important message to the broadcasted around the world regarding a catastrophic global future event. He was survived by all six of his satellites; most ascended with Punk Records into the clouds, York remained with the World Government, and Lilith escaped with the Straw Hat Pirates and is attempting to resurrect Vegapunk via cloning.

(Source: One Piece Wikia)