Louis Tully is an accountant who lived down the hall from Dana Barrett, in an apartment building on Central Park West. Five years later, he became the Ghostbusters' accountant.
In 1984, Louis Tully is a resident of the Shandor Building at 55 Central Park West and is on the 22nd floor. Louis occupies 2202. He has unreciprocated romantic feelings for Dana Barrett and clumsily bursts out of his apartment whenever she is in the hallway. He is mysteriously locked out of his apartment numerous times, unaware of the supernatural history of the building.
One night, Louis was hosting a party in honor of his fourth anniversary as an accountant. At the time the Terror Dogs, Vinz Clortho (The Keymaster) and Zuul (The Gatekeeper) had escaped from their statues and began to search for host bodies. Vinz found its way into Louis' bedroom. After Louis unknowingly tossed the coats of Ted and Annette Fleming onto Vinz, it disrupted the party, smashing through the closet door terrifiying the guests and chased Louis until it cornered him in Central Park outside the Tavern on the Green. Louis fainted when Vinz roared at him after which the Terror Dog possessed him.
Louis, now inhabited by Vinz Clortho, ran around Central Park harassing random people in search of Zuul, The Gatekeeper. He bumped into a Coachman who gave him a hard time for talking to his horse. The possessed Louis growled at him as his eyes flared purplish-red. He ran off rambling incoherently about the coming of Gozer. He later was picked up by the Cops, who in turn dropped him off at the Firehouse. Egon Spengler took some P.K.E. readings and took custody of him. Egon scanned Louis' brainwaves and saw an image of the demonic Terror Dog's head on a screen hooked up to the device. Louis introduced himself as Vinz Clortho and explained his purpose to Egon Spengler and Janine Melnitz. Following Mr. Peck's visit and the resulting explosion, Louis escaped, staggering around amidst the chaos in New York City in search of Zuul, who had possessed Dana Barrett, until finally finding The Gatekeeper in Dana's demolished apartment. They introduced each other as Keymaster and Gatekeeper and proceeded to meet at the center of Dana's ravaged apartment in a passionate embrace, kissing lustfully before heading up to the rooftop. Louis and Dana later consummated their demonic union atop a large stone table in front of the Temple of Gozer, later transforming back into their natural Terror Dog forms. After the Ghostbusters battled Gozer, Louis was released from his possession as the Keymaster and returned to normal. Egon, Ray Stantz and Winston Zeddemore helped Louis get out of the charred remains of Vinz.
At some point between 1984 and 1989, Louis earned a law degree at night school and expanded his specialties as a tax attorney. On occasion, he would work on probate. In late 1989, at Peter's insistence, Louis reluctantly becomes the defense counsel for the Ghostbusters. Despite only being versed in Tax law, he won the case due to mitigating circumstances. After the Ghostbusters went back in business, Louis was part of their staff as personal accountant and tax attorney, even going so far as to appear in one of the TV ads. At one point, Louis catches Slimer eating his lunch and both flee in opposite directions screaming.
During the week of New Years Eve, Louis finally struck up the courage to ask her out on a date. Janine was busy with babysitting Oscar but asked him to come along. While babysitting with Janine at Peter's apartment, the two became closer and made out on the couch. Oscar was kidnapped. After Dana left to go to the museum, Louis went to the Parkview Psychiatric Hospital to rescue the Ghostbusters. He returned to the Firehouse and with Janine's help, suited up in one of Egon's Uniforms and then left by foot with a Proton Pack on. Underestimating the weight of the equipment, Louis quickly became tired. He was saved by the timely arrival of a city bus that Slimer had commandeered, patching up their incident earlier. Shortly upon his arrival at the museum, Louis starts blasting the Slime Shell covering it as Vigo became weakened from revelers' singing. Upon the defeat of Vigo, the slime shield dissipated, and the crowd hailed Louis as a hero even though he had little to do with the situation.
Louis held onto Egon's coveralls as a memento of his experience during the Vigo incident, and hung up behind his desk in the lobby. He apparently switched the label from Spengler to Tully. In anticipation of the Ghostbusters offering franchising, Louis was tasked to scout locations around the USA, including Chicago, Los Angeles, and Cincinnati. During the start of the Thanksgiving 1991 holiday weekend, during the time when The Rookie was hired, Louis was not at work. He had not been feeling well and left work early, leaving a note on his desk informing the others. If the work piling up on his desk is any indication, Louis has been sick for several days, at least.