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 beauty and kindness. According to her siblings, her most annoying habit is saying "like", which is ironic, as she doesn't actually say it that often.
Despite being the second-oldest of the Loud children, Leni is a stereotypical ditzy dumb blonde and is very forgetful, absent minded, perky, and ignorant. 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 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 ignorant and absent minded, she'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 the kindest and sweetest out of the bunch, and gets along well with her siblings.
She suffers from arachnophobia, as seen in "Left in the Dark", and "No Guts, No Glori". 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 an exterminator comes 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 has 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".
"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.
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 white sunglasses on top of her head.
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.
Leni wears her sunglasses atop her head in every episode she appears in. She only removes them when she goes to bed, showers, or goes swimming.
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.
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.
The 11 of Hearts
In the minicomic Deuces Wild!, 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 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.
Leni is named after Lennie Small, a character from John Steinbeck's novel "Of Mice and Men".
Leni and Lily are the only Loud sisters who have blonde hair with a creamy tone to it.
Lori, Leni, Lucy, Lisa and Lily are the only Loud siblings not to have grayish-purple eyelids.
Her name ironically translates to "Bright", although she's not that bright.
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, who was not only mentally disabled, but also a big, muscular man who didn't know his own strength.
In "Space Invader", Leni says that she likes to brush her hair 50 times a day, but she can easily lose track.
In the first half of Season 1, Leni wore a magenta sleep mask to bed, but as of "One of the Boys", her sleep mask is blue, with a closed eyes image over it. Sometimes, she retains her magenta mask, but with the same image.
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.
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.
She is one of four Loud sisters to wear earrings (in Leni's case, hoop). The other three are Lori, Luna, and Lola.
Leni is the first sister to have her younger self shown, in "Hand-Me-Downer".
She and Lori are the only sisters who have visible breasts.
Leni, Lori, Luna, Lana, Lola, and Lily are the only siblings who don't wear socks.
Leni and Lola are the most feminine of the Loud sisters.
Leni is the first Loud sister to appear on a title card.
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 "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. This makes sense, given that she, and the movie's title character, Elle Woods, are both fashion-obsessed, ditzy blondes.
Another thing that makes Leni and Elle similar is that they're both much smarter than they first appear, as certain episodes show that, despite Leni's generally ditzy, unintelligent behavior, she's much 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.
Leni, along with Lincoln, Lola, and Lynn, are the only siblings with any knowledge of cooking.
According to the "Ask Lincoln" section on Instagram, the primary reason that Lincoln likes wearing the color orange is because 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.
"Change of Heart" reveals that Leni thinks there are only 40 states in the United States.
Her Polish name is Honorata, and she is nicknamed "Honia".
Leni's Polish dubber, Julia Kołakowska, also voices Haiku.
Interestingly, Lynn and Luna's friend Tabby, are also voiced by the same voice actress in the Polish Dub, Agnieszka Fajlhauer.
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.