At 16 years old, Leni is the second oldest child of the Loud family, and the second-oldest of Lincoln's five older sisters. She is very naive and quite ditzy, but she makes up for it with her beauty and kindness. Leni is a junior at Royal Woods High School and attends school with her siblings Lori, Luna, and Luan.
Despite being the second-oldest of the Loud children, Leni is quite ditzy and is very forgetful, absent-minded, and perky. Various examples of her simple-mindedness are expressed throughout the series. In "Linc or Swim", she does not know the rules of the game, "Marco Polo", much to Luan's annoyance. In "Project Loud House", she is shown to be unable to walk and chew bubble gum at the same time. In "Changing the Baby", she gets stuck in Lily's crib and thinks that it's a baby prison. When she's being interrogated by Lincoln and Lucy in "Sleuth or Consequences", she thinks they're interviewing her, and states that her favorite color is "zebra".
Despite being ditzy and absent-minded, Leni's shown to be skilled at fashion designing, wood carving, singing, lock-picking, and making smoothies, which demonstrates that while she may not be very bright, she is creative and artistically inclined. She is also very friendly and gets along well with her siblings.
Leni suffers from arachnophobia, as seen in "Left in the Dark", "No Guts, No Glori" and "Future Tense". This phobia is most prominent in "Along Came a Sister", where Lincoln brings his class's pet spider, Frances, home. When Leni first sees Frances, she panics and attempts to kill her with bug spray. Later on, it is revealed that Frances is still alive, and Dad – who also exhibits arachnophobia – hires an exterminator to dispose of her. Leni faces her fear and cuts off the exterminator, in order to save Lincoln's reputation – once again – showing that she does have a big heart.
Leni has also proved that she can be irresponsible, as shown in the episode "Cover Girls". She agreed to cover for Luna, Luan, Lynn, Lucy, Lola, and Lana, and later passed the task onto Lincoln. However, Leni is shown to be very compassionate, as she was the only one of her siblings to prioritize helping her family get better, as opposed to getting away when the Loud family caught the flu in "One Flu Over the Loud House". In addition, in "No Spoilers", it is shown she is the only person in the family considerate enough in the family to be able to make the perfect surprise party because she pays attention to what people like (excluding the surprise part since she always spoils the surprise because she can't keep a secret and is rather ditzy and naive).
Leni Loud loves designing outfits and accessories to go with them. Leni's easily distracted by shiny objects, and often walks into walls while talking, but what Leni lacks in smarts, she makes up for in heart. She's the sweetest Loud around!
Leni has long, pale-blonde hair, with side-swept bangs, and three pairs of eyelashes. She is almost as tall as Lori, but taller than all her younger siblings.
Her main outfit is a seafoam green dress, with white frills, and triangular sleeves. With this, she wears red hoop earrings, white sandals, topped with light green bows, and a pair of rounded white sunglasses with black lenses on top of her head.
One interesting note about what Leni wears is that the color of the bows on her sandals change to correspond with what she's wearing. In "Ties That Bind" and "Brawl in the Family", the bows were blue to correspond with the tank top and dress she was wearing. In "Tricked!", the bows were white to match the circa 18th-century dress she was wearing while as Marie Antoinette.
Leni's swimwear is also seafoam green with white frills, only it is a two-piece garment. The top half has two simple straps, while the bottom half is longer than the top, and has four white buttons. Instead of sunglasses, she wears a seafoam green swimming cap, with a white bow tie. She retains her earrings and sandals, even while in water.
Her night attire consists of a seafoam green nightgown, that looks very similar to her regular outfit but sleeveless. She also sleeps with a magenta sleeping mask, but later on, it changes to a blue mask, with an image of closed eyes over it. She retains her magenta mask, and like the blue one, it has the closed eyes image.
Leni's original design depicted her with a light blue dress, snow boots, as opposed to sandals, and a hairstyle that resembled Lori's, but was slightly longer.
In "Hand-Me-Downer", she was seen as a younger girl, but her wardrobe wasn't entirely different. She still wore a seafoam green dress and sandals with green bows on them. The only differences are that her dress didn't have frilled sleeves, and she didn't have her sunglasses.
In "Selfie Improvement", she was seen as a younger girl again. She wore a seafoam green shirt, brown cargo shorts, white socks, and seafoam green shoes.
Leni wears her sunglasses atop her head in every episode she appears in. She only removes them when she goes to bed, showers, goes swimming or goes outside in the snow.
Her sunglasses are white, with two black circular lenses, and a shine going across both of them.
When she was portraying a cat in the family play in "Suite and Sour", her sunglasses were triangular in shape, rather than circular, which looked like cat ears. This could mean that she owns more than one pair of sunglasses.
There is an animation goof that has occurred a few times, where her sunglasses are missing in one shot, and then reappear in the next shot.
In the alternate dimension where Lincoln has brothers instead of sisters, Leni is a boy named Loni. Like Leni, Loni is ditzy and dumb. Unlike Leni, he is thoughtless, and couldn't care less if Lincoln or his other brothers were hurt.
In the second alternate universe, where it's one girl and ten boys, Loni's shown to be very caring towards Linka, Lincoln's female counterpart--in fact, Loni's the one who makes the offer of him and the rest of the brothers staying with Linka until she falls asleep after they heard her screaming in the middle of the night.
Loni eventually turns out to be a product of Lincoln's imagination as it is revealed Lincoln's whole adventure was just a dream.
After finding a hotel worker's name tag in "Suite and Sour", Leni immediately likes the look of the tag and decides to put it on, fooling every hotel customer that walked by her, as the name tag says "Fritz". When the customers start to treat Leni like an actual worker, Leni decides to work as one too, giving her customers the keys to their rooms, and addressing the customers' complaints. She even tried to kick the Loud family out of their room because of reports from angry customers.
The 11 of Hearts
In the minicomic Deuces Wild! and its animated adaptation, Leni takes on the identity of the superheroine "The 11 of Hearts". She plays the role of one of Ace Savvy's sidekicks. Her signature weapons are heart ties with which she uses to tie up her foes. In the comic, she is summoned by Savvy alongside the rest of his deck to help him and One-Eyed Jack to defeat the gas monster. After they defeat it, they prepare to fight against a garbage monster.
The 11 of Hearts appears once again in "Pulp Friction", along with the rest of the Full House Gang. During her appearance in the episode, she saved Ace Savvy and One Eyed Jack from falling into a shark pit by using her pink bow as a rope.
In the episode, "White Hare", where Lincoln imagined how difficult it is to live with 15 extra sisters, Leni is a rabbit named Blair. Like Leni, Blair is a fashionable rabbit with high knowledge of what clothes are most appropriate to wear. Unlike Leni, Blair seems to be smart rather than ditzy, as there was no moment where she was doing something dumb.
Leni was originally going to be an eight-year-old girl who "didn't know her own strength", before being changed to a stereotypical teenage blonde. Her appearance was also completely different; she was obese, and had brown hair pulled into pigtails.
Her original personality is also reminiscent of Lennie Small from John Steinbeck's novel Of Mice and Men, who was not only mentally disabled, but also a big, muscular man who didn't know his own strength.
She is also named after Leni, a nurse in Franz Kafka's The Trial, who falls in love with the main character Josef K. despite his unexplained status as a felon.
In "Driving Miss Hazy", Leni is shown to have great woodworking skills.
In "Space Invader", Leni says that she likes to brush her hair 50 times a day, but she can easily lose track.
When Leni is seen walking, she almost always has her eyes closed, a big smile, and holds her hands up. A running gag is that Leni bumps into walls when she's walking, a possible result of her walking with her eyes closed.
This was brought up in "Fool Me Twice", when she taught her stunt double how to walk into a row of lockers.
Although Leni and Luan are very close, Leni believes that Luan's hair scrunchie is a "fashion nightmare".
Leni's hair is the lightest shade of blonde of all the blonde sisters, along with Lily.
In "House Music", it shows that Leni can carry Lincoln with just one arm.
Leni's strength is further shown in "Health Kicked", when she hangs by one arm while holding Lily in her other arm, and Lisa holding on to her leg.
In "A Tattler's Tale", it is shown that in addition to her fear of spiders, Leni is also afraid of rats.
Leni is one of three siblings who caused a blackout. She caused one in "Overnight Success", while the other two are Lincoln in "Left in the Dark", and Luna in "A Tattler's Tale".
In the comic "After Dark", during the story "Midnight Melody", it is revealed that Leni is a sleepwalker.
In "Job Insecurity", it is revealed that Leni wants to get her belly button pierced, but her father forbids it.
According to episode 20 of the Nick Animation Podcast, Leni's favorite movie is Legally Blonde.
She is similar to the movie's title character, Elle Woods, who also is a fashion-obsessed ditzy blonde. In addition to that they are both much smarter than they first appear, as certain episodes show that, she is just as smarter than her siblings realize.
In "Lock 'n' Loud", it's revealed that her life's work is a six-piece children's jigsaw puzzle.
She's the second-oldest, but the least intelligent of her siblings. Alternatively, Lisa is the second-youngest, but the most intelligent of her siblings.
According to the "Ask Lincoln" section on Instagram, the primary reason that Lincoln likes wearing the color orange is that Leni claims that the color looks good on him.
It is implied that Leni inherited her arachnophobia from Lynn Sr.
In "Job Insecurity", it is revealed that Leni knows about Russian cuisine.
In "Change of Heart", Leni thinks there are only 40 states in the United States.
In fact, there used to be 40 states, but for only six days, from November 2 to 8, 1889.
In "Racing Hearts", she did not know the meaning of the Spanish word "nada", when Luna said that she and Sam have nothing in common.
In the Loud House quiz, "Which Loud Sibling Are You?", her name is misspelled as "Lenni".
Leni sometimes mistakes something for her own flatulence and will apologize thusly, as seen in "No Spoilers" and "Washed Up"; this is in contrast to Lori, who often farts and claims it was something else (such as her shoe).
Her Polish name is Honorata, and she is nicknamed "Honia".
Leni's Polish dubber, Julia Kołakowska, also voices Haiku.
Leni's Russian dubber, Anastasiya Lapina, also voices Rita, Lori, Lola, Lily, and Ronnie Anne.
Leni's Italian dubber, Giuliana Atepi, also voices Lisa.
Leni's Swedish dubber, Mikaela Ardai Jennefors, also voices Luna.
Leni's German dubber, Daniela Reidies, also voices Lynn.
Leni's Portuguese dubber, Leonor Alcácer, also voices Luan, Ronnie Anne and Mrs. Johnson.
Leni's Finnish dubber, Susa Saukko, also voices Lola.
The pronunciation of her name in the Dutch dub is slightly different, being pronounced 'Lay-nee'. She is the only Loud family member that has her name changed in any way.