Llewellyn "Louie" Duck is the one of the three main deuteragonists in the 2017 DuckTales series and is the youngest of Donald's triplet nephews.
He is the most easygoing and laid-back brother, jokingly described as the "evil triplet", due to his greediness.
Donald Duck reluctantly leaves his nephews Huey, Dewey and Louie with his estranged uncle Scrooge McDuck, while he goes on a job interview. After Scrooge locks the boys into a room for making fun of him, the triplets come across Webby Vanderquack who befriends them and shows off a collection of relics and artifacts that Scrooge and Donald found during their previous adventures, only to accidentally release various ancients evils housed in them. After the kids help him to contain them back.
Huey, Dewey and Louie decide to take Webby to Funso's Fun Zone. However, due to the fact that she was locked in the Manor for almost all her life.
After seeing a scary movie, Huey, Webby, and Lena explore an abandoned subway line in search of legendary creatures and end up trapped there with the others (Mrs. Beakley, Louie, Dewey and Launchpad). As they struggle to escape, discover that the creatures are real.
During their search for The Temple of the Golden Cricket, Scrooge, the kids, and Donald make a stop at a casino resort in Macaw to meet with Donald's cousin, Gladstone Gander. Louie starts hanging out with Gladstone, resulting in Donald competing for his nephew's attention. Meanwhile, Scrooge and the rest of the kids start looking for the exit, but the owner of the casino, Toad Liu Hai, keeps distracting the kids with different gifts.
Scrooge, the kids, and Launchpad enter an Egyptian pyramid, in search of the treasures of mummified pharaoh, Toth-Ra, but got separated. Louie and Webby are imprisoned by Toth-Ra himself while the others try to gain the support of the pharaoh's servants' leader, Amunet.
Scrooge, the kids, and Launchpad spend their Christmas attempting to climb the "unclimbable" Mt. Neverrest; a task Scrooge failed at seventy-five years ago due to his treacherous guide, George Mallardy. Along the way, Launchpad is conned by a salesman into thinking that he's dying of "ice-fever" to buy some of his stuff to which Louie pulls off his own scam to expose the salesman as a fraud.
Scrooge and his family crash on the Island of Ithaquack, home of the Greek gods, where Dewey and Webby search for The Spear of Selene to uncover the mystery of Della's disappearance.
Scrooge and Glomgold compete in the "Duckburg Millionaires' Club Golf Invitational" in the Scottish Highlands, assisted by the kids and Launchpad. However, the game is hijacked by ancient druid spirits and turns lethal, with petrifying mists and two drowning-obsessed kelpies, Briar and Bramble.
On Dewey's made-up holiday, "Only Child Day", the boys split up and spend the day pretending to be only children. Huey teaches Burger and Bouncer Beagle how to be good Junior Woodchuck Scouts, Louie attempts to befriend spoiled, insane child billionaire Doofus Drake, and Dewey records an episode of his late-night talk show, "Dewey Dew-Night", as Webby attempts to keep them all together. Louie tries to tell Huey and Dewey that Tenderfeet, the Bigfoot they found, is a con.
Dewey struggles to keep his search for Della a secret from Huey and Louie. Upon Dewey’s eventual confession, Huey and Louie are left heartbroken, but eventually forgive him. Working together, they find an image of The Spear of Selene.
Louie and others continue their investigation of Della, but the adults eventually stumble upon it. After Dewey endangered himself for a clue, Scrooge reveals the truth: Della disappeared in space while piloting a spaceship he built for her, The Spear of Selene, causing Donald to cut ties with him. The boys blame Scrooge and the resulting argument causes the plane to crash. Once home, the boys move back in with Donald while Mrs. Beakley takes Webby with her on an extended vacation, leaving Scrooge in solitude.
Webby, Launchpad, and Mrs. Beakley convince Donald and the boys to forgive Scrooge. Magica reveals herself to all of Duckburg by releasing everyone's shadows and have them attack the city. Joined by Gyro, Fenton, Little Bulb, and Manny the Headless Man-Horse, Donald, Mrs. Beakley, and Launchpad fight back against Magica while the kids search for Lena. At her home, they discover she's a shadow created by Magica, and they rush to the Money Bin to stop her.
He and his family reunites and a newscast about them is viewed by Della, who's stranded on the Moon.
Tired from the constant adventuring, Louie attempts to avoid another one by proposing a family game night, causing Scrooge's competitive nature to kick in. Louie panics and uses the shrink-ray on Gyro to silence him. He then convinces Huey to help him keep the others in the dark about the increasingly hostile Gyropudlians, but things escalate during a game of "Scroogeopoly". In the end, Louie steps up and saves the day, gaining Scrooge's respect.
Louie and Webby stumble upon him and investigate, only to find no record on Glomgold before he moved to Duckburg. They then take Scrooge to meet him, but he decides to let him be, as he is happy.
He and his family visits a Brazilian town to celebrate the mysterious festival, "The Feast of The Flower." Webby tries to get Dewey and Louie to fully experience the festival, but they just want to take pictures. They all soon discover that the town's friendly locals are all part of a giant carnivorous plant.
- This incarnation of Louie uses the first name "Llewellyn" instead of Louis.