Jack Hardemeyer was the Mayor Lenny's assistant in Ghostbusters II until the Mayor finally and promptly fired the weasel for throwing the Ghostbusters into a psychiatric hospital and not looking out for the Mayor's best interests during the Vigo incident. He is also the secondary antagonist of Ghostbusters II.
At some point between 1984 and 1989, Mayor Lenny appointed Jack Hardemeyer to be his principal aide. In late 1989, after an airing of "The World of the Psychic," Peter Venkman saw Mayor Lenny and his procession moving through the TV studio. Peter attempted to go say hello but he was stopped by Jack. Jack taunted Peter by looking around for ghosts then warned him to stay away from the Mayor. Jack didn't want the Mayor to be associated with two-bit frauds and publicity hounds just as he was about to start his run for Governor the next year. Peter took his rudeness as opportunity to fire back how officials such as him are supposed to lie and figuratively kiss voters' butts.
At the Ghostbusters' trial, Jack made a brief appearance. He asked The Prosecutor to put them away for a very long time. The Prosecutor didn't think that would too hard with the list of charges. Jack then gloated in front of Peter and left the courtroom. However, due to the manifestation of the Scoleri Brothers, the Ghostbusters had all charges dropped and their preexisting judicial restraining order dismissed. With the Ghostbusters went back into business, Jack groaned in disbelief.
On New Years Eve, Mayor Lenny and Jack were pulled from a party at Gracie Mansion to speak in private with the Ghostbusters. Jack didn't believe any of their claims about Vigo and the Psychomagnotheric Slime. After Lenny refused to help and left the room, the Ghostbusters mused they should go to the press. Jack became alarmed and overstepped his authority by having them committed to Parkview Psychiatric Hospital in order to protect the Mayor's interests. Jack lied to the Psychiatric Doctor and issued orders to keep the guys under strict observation for the next several days.
As New Years approached, the city was plunged into chaos from a massive spike in paranormal activity. Jack was unable to effectively coordinate relief. When Mayor Lenny arrived at New York City Hall, he resigned himself to calling the Ghostbusters for help. Jack was forced to admit he had them committed. Lenny fired Jack and had Harry promptly remove him from city hall. Jack was last seen in better spirits, singing along with carolers at the art museum vigil.
Jack Hardemeyer is the central antagonist in a sub-plot that runs through the collection of stories in Ghost Busted. Jack was once the youngest state prosecutor in New York history and parlayed that into his position as the Mayor's aid. He dreamed of becoming Mayor even. After the Vigo incident, Jack was "blackballed everywhere, from here to Hoboken" and now homeless since being fired. Jack broke into a condemned Shandor Property and strikes up a deal with the building's resident ghosts to get rid of their shared enemies, the Ghostbusters. Providing schematics of the Proton Packs and with technical assistance from the ghost of Professor Harold Teplitz, Jack creates an electron-powered variant of the Ghostbusters' proton-powered equipment designed to stun and contain living souls, leaving the human body comatose.
Arming the ghosts with the electron equipment, Jack leads his allies to the capture of Ray and Egon while they are out on routine cases, then lures Peter and Winston to an ambush. While Peter is captured, Winston manages to escape in his own car and follow Jack back to the building hideout. Using his own collection of firearms to destroy the electron packs, Winston manages to rescue the other three Ghostbusters, and the whole team proceeds to capture the ghosts. During the mayhem, Jack cuts his losses and runs away unnoticed. He is last seen in a soup kitchen, groaning about being served split pea soup... again.
After being fired by Mayor Clotch, Hardemeyer was hired by the B.U.F.O. along with Walter Peck. News of the hire was featured on "The Pacific Monthly" Issue #15. A copy was framed and is up in Peck's Paranormal Contracts Oversight Commission office. Hardemeyer is also on Peck's speed dial.  
Jack began working for the Commission as liaison to the New Ghostbusters. Peck had problems to solve in the wake of the Ghostbusters' disappearance, mainly securing alternate paranormal contractors, convince City Hall of the wisdom of his judgement, and maintain some measure of control. Tying a merchandising deal would cover all those bases. Peck brought Jack in to serve as interim PCOC liaison. Peck allegedly warned Jack not to get carried away and gave carte blance to cut whatever deals he could. Jack called in a lot of favors to get merchandising deals secured. His primary duty was to help coordinate the New Ghostbusters' caseload.
Jack showed up on Monday and his first act was a photo shoot. Going off research, Jack made the team wear coveralls with shorts. Janine heavily objected but Jack reminded her it was covered in the contract she signed with Peck. He was already thinking of taking them on the talk show circuit. To add insult to injury, Jack also had the regular coveralls and the rest of the original team's personal effects put in storage. Janine further objected to wearing the new coveralls out in public but Jack implored them to take care of Gareth Dibello. After the team captured Dibello, Jack was ecstatic to discover three talk shows in a bidding war over the first exclusive interview with them. Janine, however, directed him to their scratched up legs. Not quite understanding, Janine made it clear she would go on the talk shows and out him as a sexist ratbag if he didn't get the regular coveralls back. Jack proposed putting Ron Alexander in shorts as well but Janine simply pulled harder on his tie, cutting off his circulation. Jack agreed to Janine's request and promised to have them back the next day.
Jack continued with procuring lucrative contracts. He was in talks with making the New Ghostbusters spokespeople for Yummy Yummy Snack Cakes and set up a meeting the next week with toy people. He was intrigued with news of a Grendel coming to kill Janine and wanted to make an event of it but the team managed to dodge telling him the place and time the Grendel would manifest. Jack still insisted Janine be outfitted with something flashy in the inevitability the battle would attract media coverage. He wondered off in thought and mused the New Ghostbusters should appear in local talk shows.
Later in the summer, Jack secured a deal for the Ghostbusters to sponsor army boots and thought the slogan "They're not just for your mother anymore!" was a real winner. Peck called Jack into his office and abruptly told him to cancel all deals made because the Ghostbusters were back in control of their brand and merchandising. Since Janine was back to coordinating with PCOC, Jack was no longer needed either and was fired. Jack realized he was being used the whole time despite being kindred spirits and friends with Peck. Peck admitted they weren't friends and only shared a hatred for Peter Venkman. Jack informed Peck he would be hearing from Jack's lawyer and stormed out.
Jack's role was similar to Walter Peck's in the first movie in that he was a skeptic who threatened and antagonized the Ghostbusters with legal and political power. As with Peck, Jack had received his comeuppance by film's end, in the form of an embarrassing and somewhat public loss of face. Similarly, he also had a patronizing first encounter with Dr. Peter Venkman. He was last seen in better spirits celebrating the new year among the crowd outside the Manhattan Museum of Art.
- In the February 27, 1989 version of the Ghostbusters II script, Jack was sucked into the slime shell surrounding the Manhattan Museum of Art. 
- In the Ghostbusters II deleted scene Jack Buys It, Peter gives Jack the nickname "Mr. Hard-On". 
- In the Ghost Busted manga, Jack wears contact lenses and owned a scooter.
- Jack Hardemeyer (1999). Ghostbusters II, Chapter 2: "World of the Psychic" (1989) (DVD ts. 11:12-11:13). Columbia Pictures. Jack Hardemeyer says: "I'm Jack Hardemeyer. I'm the mayor's assistant."
- "Ghostbusters Issue #4" (2011) (Comic p.6).
- "Ghostbusters Issue #14" (2012) (Comic p.7).
- 2/27/89 Script, Page 97 via Spook Central
- Peter Venkman (2014). Ghostbusters 1 & 2 Gift Set (2014), Ghostbusters II, Jack Buys It (1989) (DVD ts. 00:31-00:36). Columbia Pictures. Peter says: "Yes, we tried to tell you last night but we got locked up in the loony bin by Mr. Hard-On."
- Ghostbusters II
- Real Ghostbusters Starring in Ghostbusters II
- Ghost Busted
- Chapter 2
- Chapter 3
- Chapter 4
- Chapter 5
- Chapter 6
- IDW Comics