- “Oh, Louis would give anything to be up there jammin' with the big boys...”
- ―Louis expresses his dream to be a musician
Early on in the story, Louis was meant to be so cowardly, phobic, and timid that even frogs can frighten him. Eventually, however, directors John Musker and Ron Clements changed the character into what is seen today.
Also, according to The Princess and the Frog's DVD commentary on the film, Louis was, at one point, meant to be a human with a passion for music. However, he was a terrible musician and eventually went to Dr. Facilier to gain the ability to play the trumpet through magic. Facilier gave him the ability, but turned him into a gator as well, leaving Louis stranded in the bayou trying to find a way to reverse the curse just before meeting Tiana and Naveen. The idea was soon dropped for being too complicated for the story.
In earlier stages of the film, Louis' design was in the "cartoony" variety, as Goldberg states, and was seen with a slightly thinner body, more human-like features, and a pair of glasses; this echoes the original concept of Louis being a human turned into a gator by Dr. Facilier. When the story altered, Eric Goldberg used both the references of real-life alligators and the consult of his fellow animators, to arrive at the final design of the gator.
Despite his size and ferocious appearance, and unlike the vicious, hot-tempered alligators Tiana and Naveen are attacked by when they first arrive in the bayous, Louis is a gentle giant with a heart of gold. He is very fond of his trumpet and his dream is to become a famous jazz singer who can perform in front of a human audience without scaring anyone. He believes the only way to do this is to become human himself, prompting the gator to join Tiana and Naveen to find Mama Odie. He is notable for having a few phobias, though they prove to be understandable. The most notable of which being his fear of guns and the hunters that wield them; this stems from when he jumped onto a riverboat to play with a band, only to jump back into the river amidst a hail of bullets from the understandably terrified passengers. Along with that, Louis has a great fear of "pricker bushes" and traps set throughout the bayous for gators, tying in with his fear of hunters.
Despite being generally known as a coward, Louis has still proven to be quite upbeat and lively a lot of times, specifically when he's in a good mood or has the urge to play his trumpet. He has also shown to have quite the knowledge about humans and their culture. With riverboats constantly making their way through the bayous of New Orleans, Louis has received the opportunity over the years to familiarize various jazz tunes, eventually becoming the masterful trumpet player he is. Aside from music, he also knows quite a lot about human food, which is also shown to be another love of his.
Louis is a large, overweight alligator taller than a grown man with olive-green scales, dark green spines, and yellowish-green underbelly scales that stretch from his muzzle to his tail tip. He contains large rows of sharp teeth in his mouth, some of which stick out even when his mouth is closed. Louis also has yellow eyes, but unlike the other alligators found in the bayou, Louis has rounded, cartoonish pupils instead of the slit shape found in real-life alligators.
Louis first meets Tiana and Naveen when they are stranded in the bayou as frogs. The duo is terrified of Louis when they first see him, thinking he is about to eat them as he approaches them with his mouth wide open, but Louis reveals his friendly nature by identifying a jazz tune Naveen was playing on his ukulele. Louis tells Naveen of his dream to be a famous jazz player in New Orleans but explains that his last attempt to play with humans ended with his audience panicking at the sight of an alligator. When Tiana and Naveen explain that they are actually humans under a frog curse of a voodoo witch doctor, Louis, knowing about voodoo, tells them about Mama Odie, the voodoo queen of the bayou who might be able to help break the curse. At first, Louis is too scared to take them to the deepest, darkest part of the bayou where she lives because of the dangers there, but is convinced by Naveen that she could make Louis "smaller and less toothy," so that he can play music for humans without scaring them; Louis decides to ask Mama Odie to turn him human.
In the excitement of the oncoming future, Louis, Tiana, and Naveen sing about what life would be like once they're human. During the journey, Louis learns of Tiana's dream to open a restaurant, and appears to be very excited about the idea, mostly because of his great love of food. However, after getting lost in the swamp, they meet a Cajun firefly called Ray, who helps guide them to Mama Odie's home. In the mix of their journey, the group encounters a trio of frog hunters, stunning a fearful Louis, who jumps into some pricker bushes to hide and screams in pain upon doing so. After Tiana and Naveen manage to defeat the hunters, Louis' injuries force the journey to come to a slight halt, as Ray needs time to remove each thorn from Louis' butt. As they rest, Louis bonds with his three new companions, and comes to support Tiana and Naveen as lovers. During the bonding, however, the gang is attacked by a hoard of shadow demons, sent by Dr. Facilier, to kidnap Naveen. Louis, Tiana, and Ray chase after Naveen until a mysterious being arrives and defeats the shadowy creatures with ease. Louis looks upon in fear as the mysterious being is soon revealed to be the eccentric Mama Odie.
Mama Odie (who isn't as fearsome as Louis initially assumed) tells Tiana and Naveen to "dig a little deeper" to find what they need, as opposed to what they want, but also tells them that Naveen must kiss a princess to break the spell. Using her magic brew, Mama Odie locates one: Tiana's best friend, Charlotte La Bouff, who is a princess due to her father being crowned King of the Mardi Gras parade. Louis then asks to be human like his two friends, but she tells him to "dig a little deeper", as well. The friends begin to head off when Louis gets the idea to have them stow away on a riverboat to get there quicker. However, Louis is noticed by a jazz band who believe him to be a man dressed in an animal costume, like themselves. As such, they invite him to play with them in the parade. Louis is thrilled and immediately joins them. During the parade, Louis notices Ray fleeing Dr. Facilier's Shadow Demons and stops playing. While one of the players asks why he stopped, Louis contemplates a choice and chooses to abandon his dream for his friends. He reveals himself to be a real gator, and fiercely chases after the shadows. Unfortunately, Louis finds Ray in a gravely wounded state in St. Louis Cemetery and immediately starts to tear up in sorrow. He recovers him, and rushes off to find Tiana and Naveen in panic.
After Dr. Facilier and Lawrence's fates are sealed and Tiana and Naveen reunite, Louis, arrives with Ray, explaining that the Shadow Man laid him low and is hurting awful bad. Ray is able to see his friends one last time before peacefully passing away thanks to Louis. The heartbroken trio attends Ray's funeral along with his Firefly Family to bid a final farewell, and Louis plays a sad theme on his trumpet as Ray's body is pushed away in a leaf with flowers into the bayou. During a moment of silence, Louis and his friends look into the night sky and notice a new star shining brightly beside Evangeline, which appears to be Ray finally reuniting with his beloved girl. Everyone is overjoyed, and the friends head to Mama Odie for Tiana and Naveen's bayou wedding. After Tiana and Naveen are pronounced frog and wife, a kiss follows, turning the two back into humans, as Tiana was now a princess through marriage. The bayou inhabitants celebrate the love and success, including Louis, who later helps Tiana buy her restaurant by growling intimidatingly at The Fenner Bros (who were the sellers of the building Tiana planned on buying for her dream restaurant), scaring them into handing over the key to the building. Once Tiana's Palace opens, Louis is finally able to live out his dream of being a famous musician, becoming the leader of the Palace's exclusive band, the Firefly Five Plus Lou, even though he is still an alligator.
In anticipation for the 82nd Academy Awards, Naveen made an appearance in an online "interview", accepting the film's nomination with pride, though an excitable Louis was quick to crash the session, believing they had already won the award.
Louis plays a major part in the game, which takes place after the events of the film where Tiana and friends are in the mix of transforming the run-down mill building into her dream restaurant. Along with many other characters, Louis participates but is more prominent in the various mini-games that take up most of the game, showing some of the adventures Louis, Tiana, and the others had partaken in during their journeys in the bayou.
Whilst not appearing in the game itself, Louis was commonly mentioned by both Tiana and Naveen during their meet-and-greet sessions with the game's players. He was prominently mentioned during a quest given by Naveen who asks the player to find a replacement band to play for Tiana's Palace as Louis went off on a gator family reunion for a while.
In Mickey's Soundsational Parade—along with Tiana, Ray, and Naveen—Louis is featured on Tiana's float, seen dancing along to the bouncy music from the film as the parade proceeds.
On Main Street, U.S.A., Louis is featured on the Enchanted Window display themed after The Princess and the Frog.
In the Magic Kingdom's Frontierland, Louis assists Mama Odie and the guests in their quest to foil Doctor Facilier, who has been revived from the dead by Hades in Sorcerers of the Magic Kingdom. Louis is first heard alerting Mama Odie about Facilier busting Lawrence out of jail and is later seen alerting Mama Odie about Facilier kidnapping Tiana. Later on, Louis assists the guests when battling Facilier for the crystal of the Magic Kingdom. After Facilier is defeated, Louis retrieves the crystal so it can be returned to Merlin.
Louis' likeness is also featured at Disney's Port Orleans Resort.
In Paris, Louis, Naveen, Tiana, and Dr. Facilier were featured in the special 2013 event, Disney Dreamers Everywhere!
In Shanghai, Louis is depicted on The Princess and the Frog-themed mosaic mural inside of Enchanted Storybook Castle.
Louis makes meet-and-greet character dining appearances at the Tiana's Place restaurant aboard the Disney Wonder cruise ship.
- In a deleted scene and the chapter book continuation of the film The Grand Opening, it is revealed that Louis named his trumpet Giselle.
- Originally, Louis was meant to be introduced after Ray, but the filmmakers felt doing so would make Louis seem like an interruption and decided to swap the introduction order between the two sidekicks.
- In some screenshots, it is shown that Louis has green eyes.
- Despite the fact that alligators have incredibly thick skin and can recover very effectively from serious injuries such as broken legs, Louis has a very low tolerance for pain as shown when he screams in agony when a thorn sticks to his finger, and when more are pulled from his rear end. Of course, this could be a placebo effect due to his meek, cowardly nature.
- When Louis says, "All kinds of hoodoo," he makes a reference to Madam Mim when he grabs some overhead vines and, pretending they are hair, parts them to show his face as he widens his eyes. He even resembles her a bit when he does that.
- Louis shares the same first name with Louis Armstrong, a famous trumpet player from the time period that the film takes place in (1920s). The alligator may have been named after him.
- Armstrong is also referenced in the song "When We're Human" from the film.
- Louis is the second Disney character who is influenced by Louis Armstrong; Scat Cat from The Aristocats is likewise and was originally intended to be played by Armstrong prior to his passing, leading to him instead being played by Scatman Crothers.
- Louis was temporarily removed from Mickey's Royal Friendship Faire at Walt Disney World due to a tragedy involving an alligator near Disney's Grand Floridian Resort & Spa, three days prior to the show's premiere. As of July 13, 2016, he has since been added back into the show.
- Real alligators have blunt U-shaped snouts and their top teeth show when their mouth is closed. While Louis' snout looks more like a crocodile's, he has only his top teeth visible when his mouth is closed just like a real alligator. Also, real alligators are black, gray, or dark blue rather than green.
- In follow-up books for the film, it is shown that Tiana and Naveen retain some of the magic from Facilier's curse, specifically their ability to talk to animals which allows them to talk to Louis.
- In Kingdom Keepers IV: Power Play, the group encounters a trio of villainous alligators, and the largest of which was said to resemble Louis. Whether or not this was a corrupted version of Louis himself was not specified.