The quick-witted, fast-talking youngest brother, Louie has a knack for charming his way into, though not always out of, danger. "The Mouth" has Uncle Scrooge's head for wild, larger-than-life moneymaking schemes, but none of Scrooge's work ethic. His keen improvisational skills are a welcome asset on any given adventure, although they sometimes land the family in even bigger trouble.
Louie is a small, white, 12-year-old duck with a green hoodie.
As been described as the 'evil' triplet, Louie is a laid-back street smart trickster and is he is always up for an adventure with his family especially if it involves treasure. Louie can be very greedy, and like Scrooge, he's got an eye for money and treasure. Although Louie has a lazy and careless personality but can be adventurous and smart when it counts.
Louie is a schemer, with his confidence and persuasive charm he manipulates others to get want he wants, as seen in Daytrip of Doom! and The Great Dime Chase. With this Louie can be seen with a con-artist persona.
Louie has also shown to be inconsiderate, as he's shown to say insensitive things like in Daytrip of Doom! where he states they shouldn't have brought Webby to Funso's right in front of her. And he did the same thing in The House of the Lucky Gander! when he calls his Uncle Gladstone their Best Uncle in front of his Uncle Donald who has raised him since they were young. Although Louie later realized how hurtful he was and then cheers on the others.
In the episode The Living Mummies of Toth-Ra!, it is revealed that his cool and slacker attitude is all a facade and that he is a scared little kid who tries to talk himself out of situations, only to get himself into more trouble and acknowledges the error of his actions. This shows that he is insecure and cowardly, and puts up a laid-back bravado as a means to hide his true feelings.
Louie is also very selfish. Louie does a lot that he knows would benefit him, like receiving money and treasure. Louie believes that most adventures include treasure, but if there is nothing to benefit him, he steps out like in The Impossible Summit of Mt. Neverrest! where once he's told there was no treasure on Mt. Neverrest he walks out on the adventure.
Donald is Louie's uncle and guardian for most of his life, and even though Louie doesn't think of him as cool, he still loves him regardless. This is well shown in the episode The House of the Lucky Gander! where he claims that Gladstone Gander, is their Best (non-rich) Uncle excluding Donald in front of him creating a jealous Donald. However, Louie realized Donald is the better uncle and then cheers him on through the rest of the race.
Louie cherishes his great uncle and holds him up in high regards especially since he's rich, and Scrooge loves him back yet Scrooge has shown to be a bit short with him. In the episode The Great Dime Chase! Scrooge is shown to be annoyed by Louie's lazy and spoiled attitude, that it made Scrooge want to teach him that hard honest work is the most rewarding. Louie seems to regard Scrooge's wealth and possessions as his own by association and has no qualms about exploiting it.
Huey and Louie are very different in fact they seem to be the opposite; where Huey is hard-working, honest plans ahead, while Louie is lazy, sly, cheats and thinks at the moment. Yet they are very close as brothers and always stick together.
In Woo-oo! Webby attacks him and his brothers, Louie thought of Webby to be weird but also interesting and they turn into good friends. Though in Daytrip of Doom, Louie sees Webby as a handful and even states this in front of her, yet he later accepts her quirkiness and they become better friends. Although in The Living Mummies of Toth-Ra!, Louie and Webby were stuck together and had to escape the many dangers of the tomb of Toth-Ra. Webby gets irritated by Louie for always seeking to manipulate situations to his own benefit, but they later resolve their issues and help each other out.
Even though Louie knows little about Lena, he does like her regardless. Although when they first met, Lena jumped him and scared him, but when she tricked the entire Beagle Family he admires her slick wits and Louie even called her his "new favorite".
His voice actor, Bobby Moynihan, has done many other voice acting roles including in Nature Cat and We Bare Bears, but he is best known for his 8 season(s) performance on the NBC sketch comedy Saturday Night Live.
It is revealed in the episode "The Spear of Selene!", that Louie's real name is Llewelyn, which he hates.