Louis Tully was hired by the Ghostbusters before the Doctor McCatheter incident. He was employed by the Ghostbusters and worked as their Accountant  and Tax Attorney, occasionally taking up a Proton Pack.
Primary Canon HistoryEdit
The Real GhostbustersEdit
As a financial specialist, Louis is known to be particularly frugal. Louis once stated he had an aversion to health food. But he did pick some up because "The price was right" (if it was free).  He does look up to the Ghostbusters and always tries to be worthy of their respect. He also likes kids and tries to be a good Uncle to his nephew, Lawrence Tully. Louis' frugality was used against him when he accepted free New Spirit Chips from McCatheter, which led to the Ghostbusters developing an allergy to ghosts. During the incident, Louis donned a Proton Pack and helped trap McCatheter.
Louis tried to prevent the Ghostbusters business from going bankrupt by giving a tour to willing investors, who unfortunately refuse to donate money to the Ghostbusters after a ten-year-old Egon Spengler throws water balloons at them.  Louis and Janine were abducted by Poso on Janine's birthday and the Ghostbusters rescued them with the help of another ghost. When the Ghostbusters were kidnapped by ghosts that consider their business a serious crime, Louis, Slimer, and Janine entered the Ghost World and rescued them. During a TV Special, Louis tried to help out by pretending to be the ghost of Al Capone. During a Halloween holiday, Louis asked Dr. Crowley what he was against other than Halloween. Later, he is seen along with Slimer and Janine trying to prevent Boogaloo's minions from opening the Containment Unit.
Louis once ended up placed in the mirror world with Slimer by Slimer's evil lookalike. During a charity race, he and Janine had to save Slimer and the Ghostbusters when they got sent to the ghost world. They succeed in rescuing them and preventing The Phantom from crossing over into the physical plane again. He was more concerned with returning the Ghostbusters' rented outfits before 5 pm and get the deposit back.  Louis played a big part in the rescue his nephew Lawrence when he was abducted and tricked by the demon Lothgar.
Louis Tully never appeared nor was mention in Extreme Ghostbusters, making him the only person who was part of the Ghostbusters to never once be referenced.
Secondary Canon HistoryEdit
Louis' tryst with Janine was never touched upon in the animated continuity, although Egon did make a barbed comment about it to her in the NOW comic book series.  However. Janine was quick to tell Egon that Louis was sweet but harmless, implying that any relationship with him was ephemeral at best. 
In his one NOW comics appearance, it seems Louis comes by to keep Janine company while Egon and the boys are out of town on a mission. He's apparently not allowed to drive Ecto-1. It is also notable that while he had brown hair in the animated series, his hair was black in the comic book.
The Real Ghostbusters MagazineEdit
Louis made a few appearances in The Real Ghostbusters Magazine. In the Spring 1990 magazine, he is revealed to have an uncle named Elwell who works on a farm.  He also wears two different jumpsuits: One colored gray with a red trim, the other colored purple with a yellow trim.
The Real Ghostbusters version of Louis, like the movies, is a nebbish. Every so often, he tries to save the day during the few episodes he's in, but never really gets the chance to pull it off. Louis on a few occasions has introduced himself as a "Tax Attorney,"  one of the few references to "Ghostbusters II" ever mentioned in the cartoon. He always carries business cards with him he will hand out when introducing himself.
- In "Something's Going Around," Louis is first shown to be frugal.
- This tied in with Louis' portrayal in the first movie when he recommended cheaper pain reliever and wrote off his party as a business expense.
- In another similarity to his movie counterpart, deep down Louis really wants to be a hero and do good.
- Louis mentions his mother in "Three Men and an Egon".  
- Louis did taxes for Peter at least once. 
- Louis hates beets. 
- At high speeds, Louis gets carsick.  
- Lawrence Tully is Louis' spoiled rotten nephew.  Like his uncle, Lawrence wears over sized glasses and a bow tie. Lawrence Tully even shares some facial features with his uncle. This also implies Louis has a brother, who probably dresses the same.
- Louis also has three action figures in the post-Ghostbusters II "Real Ghostbusters" toyline by Kenner. One has a mini-mech unit, a second had a "Slime" gimmick that appeared when dipped in water, and the third and final had a glow-in-the dark outfit and matching gear. As in the comic book, Louis' hair was black. All three figures featured an ill-fitting jumpsuit, though Louis only wore a jumpsuit in "Jailbusters" and "Something's Going Around".
- On the subscription cover of Ghostbusters Volume 2 Issue #15, Louis makes a non-canon cameo.
Since he wasn't used much past Season 5, it is fine to list were he appears
- "Something's Going Around"
- "Three Men and an Egon"
- "Elementary My Dear Winston"
- "Partners in Slime"
- "The Ghostbusters Live! from Al Capone's Tomb!"
- "The Halloween Door"
- "Trading Faces"
- "The Ransom of Greenspud"
- "Janine, You've Changed"
- Cameo - A photograph of him can be seen in the scrapbook.
- "Afterlife in the Fast Lane"
- "Busters in Toyland"
- Issue #17 (only appearance)
- ↑ Louis Tully (2009). The Real Ghostbusters - "The Halloween Door" (1989) (DVD ts. 03:45-03:52). Time Life Entertainment. Louis says: "Well, not to pry, I...I'm just an accountant, and by the way you probably paid too much for that suit but what's all this other stuff you're against?"
- ↑ Louis Tully (2009). The Real Ghostbusters - "Something's Going Around" (1989) (DVD ts. 05:29-05:33). Time Life Entertainment. Louis says: "Oh, never touched the stuff. But the price was right."
- ↑ Peter Venkman (2009). The Real Ghostbusters - "Three Men and an Egon" (1989) (DVD ts. 06:06-06:08). Time Life Entertainment. Peter says: "Oh, not another one of your schemes, Louis."
- ↑ Louis Tully (2009). The Real Ghostbusters - "Afterlife in the Fast Lane" (1990) (DVD ts. 03:38-03:43). Time Life Entertainment. Louis says: "Remember, those uniforms have to be back by five or we lose our deposit!"
- ↑ Egon Spengler (1989). The Real Ghostbusters Issue #16, p.2. Now Comics, Chicago IL USA. Egon says: "There won't be anything else you can do. It'll give you more time to spend with Louis. But don't let him drive the Ectomobile. It could be..."
- ↑ Janine Melnitz (1989). The Real Ghostbusters Issue #16, p.3. Now Comics, Chicago IL USA. Janine says: "Egon! Can't you see? Louis is sweet, but he's harmless! He just happened to be there while you were too wrapped up saving the world to pay any attention to anything else!"
- ↑ Lerner, Andrew (1990). The Real Ghostbusters Magazine Spring 1990, p.14. Welsh Publishing Group Inc., New York NY USA, ISSN 1043-3945. Louis says: "Sorry, Uncle Elwell. We'd better pack our things and leave before I wreck your whole farm."
- ↑ Louis Tully (2009). The Real Ghostbusters - "Trading Faces" (1989) (DVD ts. 06:41-06:44). Time Life Entertainment. Louis says: "Oh, Louis Tully. Tax attorney."
- ↑ Louis Tully (2009). The Real Ghostbusters - "Three Men and an Egon" (1989) (DVD ts. 17:08-17:11). Time Life Entertainment. Louis says: "Uh, sorry, Winston. I got dog obedience class tonight."
- ↑ Louis Tully (2009). The Real Ghostbusters - "Three Men and an Egon" (1989) (DVD ts. 17:14-17:18). Time Life Entertainment. Louis says: "Nuh uh, I don't. My mother felt I could use the discipline."
- ↑ Peter Venkman (2009). The Real Ghostbusters - "Trading Faces" (1989) (DVD ts. 07:16-07:19). Time Life Entertainment. Peter says: "Hey, where's Louis? He's supposed to do my income taxes today."
- ↑ Louis Tully (2009). The Real Ghostbusters - "Kitty-Cornered" (1989) (DVD ts. 19:49-19:50). Time Life Entertainment. Louis says: "I hate beets!"
- ↑ Louis Tully (2009).The Real Ghostbusters- "Afterlife in the Fast Lane" (1990) (DVD ts. 06:47-06:51). Time Life Entertainment. Louis says: "I hope not."
- ↑ Louis Tully (2009).The Real Ghostbusters- "Afterlife in the Fast Lane" (1990) (DVD ts. 06:56-07:03). Time Life Entertainment. Louis says: "Gurgk. I know but so does the fate of your upholstery."
- ↑ Lawrence Tully (2009). The Real Ghostbusters - "Busters in Toyland" (1990) (DVD ts. 03:15-03:16). Time Life Entertainment. Lawrence says: "When's my Uncle Louis coming back?"