Neville Sinclair is the main antagonist in Disney's The Rocketeer. Initially appearing as a dashing Hollywood action star, he is revealed to be a ruthless Nazi agent sent by his superiors in Germany to steal the jetpack developed by Howard Hughes in the United States.
Neville hired crime boss Eddie Valentine and his hoods to steal the rocket pack but the men were unsuccessful due to the interference of the FBI. He used his main henchman, the hulking giant Lothar, to execute the man responsible for the failure, incurring the resentment of Eddie.
Learning that the airplane pilot, Cliff Secord, possesses the jet pack, Neville uses his womanizing skills to seduce Cliff's estranged girlfriend, Jenny Blake, into giving up the whereabouts of Cliff. Neville almost had the opportunity while dancing with Jenny at a dance club until Cliff, as the Rocketeer, interfered with both Neville and Eddie's attempts at kidnapping Jenny. Despite the interference, he still kidnapped her under the pretense of protecting her, but she knocks him unconscious and tries to escape his house, only to discover his Nazi affiliations in a secret room. His allegiance exposed, he switched to a cold hearted and evil persona and ordered Lothar to bind and gag Jenny.
Neville, Eddie, and their respectice thugs called Cliff over to an observatory to demand a trade off for Jenny, but Cliff and Jenny exposed his true allegiance to Eddie who subsequently drew the line at treason and demanded Neville to let Jenny go. Sinclair laughed and summoned hidden Nazi commandos to surround the group. Fortunately, equally hidden FBI agents revealed themselves and a gun battle erupted between the Feds and Eddie's men on one side and the Nazis on the other side. Neville and Lothar took Jenny with them to an awaiting zeppelin, where Sinclair started to endure the irritating gripings of his Gestapo superior.
Knowing that Cliff managed to fly onboard and disable the rudder of the zeppelin, Neville ordered Lothar to deal with the American, only to find the unconscious body of Lothar crash through the cockpit window and knock the pilot out to his death. When his superior insulted him by calling him an actor, Neville revealed a sadistic side by shooting the Gestapo agent dead and throwing him out to loosen the weight of the zeppelin.
Confronted by Cliff, Neville demanded he release the jet pack or he will kill Jenny.Cliff did so but quickly engaged Neville in a fist fight. The fight was interrupted by Jenny attempting to shoot Neville with a flare gun which only set the zeppelin on fire. Choosing to save himself, Neville put on the jet pack and flew out, unaware that Cliff had dislodged a piece of chewed up gum on a leaking fuel tank. In a burst of flame, Neville spun out of control and plummeted with a scream into the HOLLYWOODLAND sign, destroying himself and the LAND portion of the sign.