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Walter Peck was the secondary antagonist of the first film and was an inspector for the Environmental Protection Agency, or EPA, for the third district, in the greater New York area. In Ghostbusters: The Video Game, he went on to lead the Paranormal Contracts Oversight Commission, an agency overseeing the Ghostbusters.
Walter Peck was concerned with the wild stories about the Ghostbusters generated by the media and the EPA wanted to assess the Ghostbusters' operations for any possible environmental impact, such as the presence of noxious, possibly hazardous waste chemicals created by the Storage facility that the Ghostbusters used to house their captured spirits. Peck met with Peter Venkman and things quickly became heated. Peck demanded to see the Containment Unit or he would back with a court order. Peter goaded him to get a court order and threatened to sue him for wrongful prosecution.
After Peter refused to allow him to tour the facility, Mr. Peck secured a cease and desist all commerce order, a seizure of premises and chattels, a ban on the use of public utilities for unauthorised waste handlers, and a federal entry and inspection order to tour the facility. Peck declared the Ghostbusters were facing federal prosecution for at least half a dozen environmental violations. Under pure speculation and against both the firm warnings of the Ghostbusters and an attending Con Edison worker's reticence against it, he had the grid shut down and released all the spirits back into the city. This caused a massive explosion in the process which he later claimed was the responsibility of the Ghostbusters. Egon Spengler did not take kindly to Peck's accusation and lunged at him. The Ghostbusters were subsequently arrested.
In a meeting with Mayor Lenny, Peck tried to tell him that the Ghostbusters were running a scam operation using sense and nerve gases to induce hallucinations of ghosts as well as repeating his spurious charge of them causing an explosion he himself is responsible for. However, Peck's immature fury of the Ghostbusters' contempt for him and the attending civil servants', including the Fire Chief, firm rebuttal of his claims with numerous reports of bizarre phenomena that cannot be explained as anything but supernatural completely undermined his credibility. With this support, Venkman is able to convince the Mayor of New York City of the dire threat and their readiness to attempt to stop it and Peck was promptly ejected from the office while he childishly swore revenge against the Ghostbusters. Peck was among the spectators outside 55 Central Park West when the Ghostbusters confronted Gozer. After the Stay Puft Marshmallow Man was defeated, a large amount of melted marshmallow fell on Peck and he humorously screamed out that he hated Venkman.
- In the film, Walter Peck is portrayed by William Atherton. Archive audio of Atherton's performance is used in the game, Due to Atherton being unavailable at this time.
- He has the same hairpiece as Owen.
- In the game, Walter Peck never contacts Mayor Lenny, nor gets covered in melted marshmallow.