Besides being a thief, Otto van Cooper was a great fighter ace, and mechanic.
― Sly Cooper, from inside the Cooper Vault[src]
Otto van Cooper[note 1] was one of Sly Cooper's ancestors who was a genius mechanic and skilled fighter pilot. Due to his physical ineptitude, he used his talents to pull off heists, with his machines facilitating his thievery. He had kept some of his technical blueprints in the Thievius Raccoonus. The propeller blades of his biplane were shaped like the trademark Cooper hook. His section of the book was stolen by the Fiendish Five's demolitions expert, the Panda King.
In addition to his thieving reputation, the commentary Sly Cooper made in the Cooper Vault near the end of Sly 3: Honor Among Thieves mentioned that Otto was a fighter ace. His trademark plane could be seen hanging up in his section of the vault. This section of the vault also showcases his mechanic skills, as he rigged propellers to test the intruder's reaction time, something that Otto was known for, being a fighter pilot.
In Sly Cooper and the Thievius Raccoonus, after Sly defeated the Panda King, he reclaimed Otto van Cooper's section of the Thievius Raccoonus. He utilized Otto's designs to make two modifications to the Cooper Van: a battering ram in the front, and a turret that replaced the satellite at the top of the van.
The turret was used to clear the route to Clockwerk's fortress of mines and to destroy all of the robo-falcons that swarmed the van. The gun was later destroyed because of a low ceiling that the gun smashed into. The battering ram was used to defeat fire slugs that were attempting to disintegrate computers that were falling from the ceiling in the next area, computers that Bentley needed in order to open the passage leading further into the fortress. Without Otto's designs, Sly may never have been able to defeat Clockwerk.
In Sly 3: Honor Among Thieves, the Cooper Gang built a biplane, which was based on Otto's.[note 2] Sly used the biplane in the ACES competition, and at Kaine Island to destroy several missile turrets and defeat robotic bats and Dr. M's giant Whale-Fly.
Otto was the only Cooper that was not shown to have a handheld cane stored in the vault. It remains unknown what his cane looked like. However, he had to have owned one as he needed something to get in the vault with. The only thing similar in shape to a cane that he stored in the vault was a propeller on his plane.
It is unknown why Otto perished later on, though Clockwerk was likely involved.