Task: Question Answering
Input (English): Passage: In a technologically-advanced 1939, the zeppelin Hindenburg III moors itself atop the Empire State Building. Aboard the airship is Dr. Jorge Vargas, a scientist who arranges for a package containing two vials to be delivered to Dr. Walter Jennings. The courier looks back while leaving with the vials, to see that Dr. Vargas has vanished.
Polly Perkins, a reporter for The Chronicle, is looking into the disappearances of Vargas and five other renowned scientists. A cryptic message leads her to Radio City Music Hall, against the warnings of her editor, Mr. Paley, where she meets Dr. Jennings during a showing of The Wizard of Oz. He tells her that a Dr. Totenkopf is coming for him next. Suddenly, seemingly indestructible robots attack the city. Clearly outmatched, the authorities call for "Sky Captain" Joe Sullivan, the city's hero and Perkins' ex-lover and the commander of the private air force the Flying Legion.
While Joe engages the robots with his modified Curtiss P-40 pursuit fighter, Perkins photographs from the street with little regard for her personal safety. He eventually manages to disable one robot; the rest leave thereafter. News reports show similar attacks around the globe. The disabled robot is taken back to the Legion's air base so that technology expert Dex can examine it. Polly follows and convinces Joe to reluctantly let her in on the investigation. Her information takes them to the ransacked laboratory of a dying Dr. Jennings, while an assassin escapes. Just before he dies, Jennings gives Polly the two vials and states that they are crucial to Totenkopf's plans. Polly hides the vials and withholds the information from Joe. They return to the Legion's base just before it comes under attack from squadrons of ornithopter drones. Dex tracks the origin of the signal controlling the drones and notes it on a map before his capture. 
Question: What is the alias of the person who engages the robot?
Output (English): Sky Captain.