The Engineer is a holodeck character in Emergence who tries to seize control of the Orient Express and is shot by the Hitman, an image of a conflict within the Enterprise-D's emerging mind.
The Engineer appears in the seventh-season episode Emergence. In the composite holodeck programme that the ship has created for itself, he is the driver of the Orient Express, dressed in overalls and cap.
While Data, Worf and Deanna Troi are aboard the train trying to understand what is happening, the Engineer bursts in and attempts to take over, saying that the train is being taken somewhere it should not go. He is carrying a brick. The gangster known as the Hitman shoots him and takes the brick for himself.
The crew come to read the scene as the new intelligence overriding one of its own impulses in order to keep to its purpose, in the same way that the ship has been overriding their helm commands.