According to an Instagram post from the production crew, Clyde is Howard and Harold's adoptive child. This was later proven in "Baby Steps".
Clyde is awkward, caring, nerdy, sweet, and supportive at the same time. Lincoln can always count on Clyde to help him with a plan. Like Lincoln, Clyde has a passion for comic books, video games, and science fiction movies. He is also a cat lover and owns two cats that he loves very much, even though his oldest cat Cleopawtra always misbehaves.
Clyde is quite intelligent beyond his years. He knows how to do taxes and about table manners and knows how to take care of babies because he learned about it from magazines in Dr. Lopez's waiting room. Besides, he seems mildly rich through his parents, given his nice house and lifestyle. He is socially inept, but ultimately a very friendly and kind person. Clyde is patient and enjoys the company of all of Lincoln's sisters since he gets lonely with being an only child.
Clyde is very neurotic, cowardly, cautious, and worrisome. He has asthma, which requires him and his dads to carry an inhaler everywhere. According to his parents, he cannot consume meals with too much sugar or orange juice with pulp. Clyde is allergic to certain kinds of nuts, but not peanuts, however, his dads are afraid he might later develop a peanut allergy. He is also sensitive to gluten (possibly non-celiac gluten sensitivity). He is acrophobic, and can show severe signs of altitude sickness because of it. Clyde often panics and overreacts; when he does, he hyperventilates into a paper bag that he carries with him at all times.
Clyde is a huge fan of Blarney, the show's version of Barney the Dinosaur. He knows all of Blarney's songs by heart. He also owns many stuffed animals that keep him company. Clyde has his laptop and a white noise machine in his room. He has a baseball trophy, possibly passed down from Harold (who used to be a baseball player). He also possesses both a humidifier and a de-humidifier.
A running gag in the show's first three seasons was Clyde's former unhealthy and obsessive crush on Lori. Seeing, hearing, or even thinking about her caused him to freak out, bleed profusely through his nose, and act like a malfunctioning robot in some cases. He occasionally fainted as well. In his closet, Clyde had a shrine filled with candid pictures of Lori and treasures things she gave him or touched or he stole from her. Clyde also sent Lori gifts, but Lori stored Clyde's gifts in a box. Sometimes, Clyde tried to sabotage Lori and Bobby's dates, but always failed and ended up making their love stronger. In the third season, this gag came up a lot less frequently, ultimately ending after "Absent Minded". Clyde may have finally managed to keep his excessive behaviors around Lori under control thanks to Leni's lessons. Despite this, Clyde still feels something for Lori, only that he does not prove it and does it now in a less obsessive way than in the past. After the third season, Clyde's crush on Lori seems to have disappeared definitively, as he has since had crushes on Stella in her introductory episode, and on Emma and later Chloe in "Brave the Last Dance". Meanwhile, Clyde and Lori seem to have become good brotherly friends.
Clyde is Lincoln's best friend and wingman. As an only child, Clyde is jealous of Lincoln's full house and is always willing to play his part in a crazy scheme. He has a big crush on Lori and can't act normal when she's around. Clyde spends so much time at the Loud House; he's almost an honorary sibling!
Lincoln’s partner-in-crime! Clyde is Lincoln’s right-hand man for any and all schemes, strategies, and shenanigans. They’re peas in a pod who like all the same movies, TV shows, and toys. Though Clyde’s an only child, he spends enough time with the Louds to be an honorary sibling.
Clyde wears circular glasses with thick black rims and blue-tinted lenses. He has freckles and black hair styled into an Afro. Just like Lucy, his hair always has a bright outline (although he is white and Lucy's is blue). He is normally seen wearing black pants, and a yellow-and-blue striped shirt with a white-collar. He wears black tennis shoes with three white stripes, and white laces on each.
Clyde's sleepwear consists of a blue nightshirt with a white collar and a pair of matching pants. Howard has mentioned that Clyde also owns footsie pajamas.
Clyde wears glasses. They look nearly identical to Lisa's in design and color scheme. However, Clyde's glasses are somewhat more oval-shaped and less thick. The color of the lenses is a lighter shade of blue than Lisa's.
At the end of "One of the Boys", Lincoln is sent to a second alternate universe in which every character's gender is swapped. A female version of Clyde is seen in a photo, alongside Lincoln's female version, Linka.
Girl Clyde has long black hair with a blue ribbon in it. She wears a yellow short-sleeved dress with a single, horizontal, white stripe in the middle. She also has glasses identical to Clyde's and purple hoop earrings similar to Leni's red ones. Girl Clyde might have a crush on Loki Loud, the male version of Lori, and she likely has two moms (female versions of Howard and Harold).
This version of Clyde eventually ceases to exist, as it's revealed the entire ordeal is just Lincoln's dream.
Clyde is a fan of the Ace Savvy comic books, just like Lincoln. Lincoln and Clyde have cosplayed as Ace Savvy and his sidekick, One-Eyed Jack, respectively. In the episode "Sleuth or Consequences", the boys dress up as them for a comic convention that they ultimately never attend.
In the comic Deuces Wild! and the corresponding short, Lincoln and Clyde pretend to fight a giant gas monster as Ace and Jack. They are joined by the sisters' superhero alter-egos at the end of the comic to help defeat the monster.
In "Pulp Friction", Lincoln and Clyde create a comic book for a contest and imagine themselves in the roles of Ace and Jack respectively.
In "Tricked!", Clyde dresses up as One-Eyed Jack for Halloween.
In "Deal Me Out", Clyde cosplays as One-Eyed Jack, but then he and Lincoln are made fun of for cosplaying and wonder if they are too old for Ace Savvy. However, they eventually learn that one is never too old. Clyde also mentions to a little girl that Jack is the character he tends to cosplay as, and it's revealed that he dressed as Jack for Halloween at age five.
In "Crimes of Fashion", Clyde cosplays as Jack to assist Lincoln (dressed as Ace) in trying to determine why some scarves at the mall have been disappearing.
In "Recipe for Disaster", Clyde again dresses as Jack to help Lincoln (who is, once again, dressed as Ace) investigate something. This time, they are investigating the disappearance of Lynn Sr.'s recipe book and the fact that some frozen dinners have the same recipes as Lynn Sr.'s food.
In "Kings of the Con", Clyde cosplays as Jack at a convention, along with the Loud children, who cosplay as Ace and the Full Deck.
In "Family Bonding", Rita recalls that Clyde once dressed up as Jack while helping Lincoln spy on the Louds' neighbors and believing them to be supervillains.
In "White Hare", he appears as a beaver named Danny in Lincoln's dream.
Danny is a big brown beaver with a blue and yellow striped shirt. Danny is similar to Clyde in every way: awkward, caring, nerdy, sweet, and supportive at the same time. He also seems to have an unhealthy and obsessive crush on Betty similar to Clyde's crush on Lori.
Like Girl Clyde, this version of Clyde also ceases to exist since it was just Lincoln's dream.
Calyde of the McBride Clan
In "10 Headed Beast", Clyde, in order to entertain a bored Lincoln, pretends to be a warrior named Calyde of the McBride Clan.
Calyde resembles Clyde, only fully-grown and more muscular. He also wears a different outfit: black boots with large silver rims, black shorts, a lime green belt with a large gold buckle, a lime green jerkin, a blue collar, and black arm bands with a blue hem on the bottom and a lime green hem (with a red gemstone) on the top. However, he still wears glasses.
In the fantasy sequence, Calyde gives Lincoln's alter-ego, Linc the White-Haired, help for curing his boredom by getting an object similar to a TV remote. Despite being an adult, Calyde still speaks in Clyde's voice.
The Ghost of Christmas Present
In "A Flipmas Carol", Flip dreamt of two Ghosts of Christmas Present, who resembled Lincoln and Clyde.
The ghost Clyde resembles Clyde but has no legs and wears a green elf costume.
In the dream, the two Ghosts of Christmas Present showed Flip the results of his conning. The ghost Clyde also frequently quoted Dr. Lopez to Flip.
Clyde is allergic to gluten, but he can be seen eating things with gluten in a few episodes.
According to the official The Loud House Instagram's segment "Ask Lincoln Loud", Lincoln and Clyde met by running into each other, dressed as Ace Savvy and One-Eyed Jack, respectively.
This was then confirmed and incorporated into "Deal Me Out".
In "Out of the Picture", Clyde tells Coach Pacowski that he has had nine years of therapy with Dr. Lopez. If Clyde followed Dr. Lopez's therapy for a long time, who was also Howard's therapist, this means that he probably was adopted when he was a very small baby (about 2 years old, or younger if Clyde began therapy after his adoption).
His adoptive parents have been together for 20 years. This implies that Clyde probably was adopted 8 years after the start of their official relationship.
The official Instagram page for The Loud House occasionally misspells Clyde's surname as "Clyde McBryde" in their hashtags, such as on this video, and this image.
When he had a crush on Lori, he hated the way he acted around her since he couldn't control himself when she was nearby.
He doesn't like magic shows (and only goes to them because Lincoln likes them).
Clyde is the second character to change voice actors/actresses due to their voice actor hitting puberty, with the first being Lincoln.
According to Living Loud: Surprise Party, he is allergic to dogs, hamsters, canaries, and bats. However, this information is dubious because the game also states that he is allergic to cats, which he is not, as evidenced by him owning two cats. Additionally, Clyde interacted with Charles in "Game Boys" and Walt in "Chore and Peace" and didn't have any allergy symptoms.
This game also suggests that he's scared of climbing through air vents.
He claims to have bad depth perception, though that may have been because he was wearing an eye patch at the time. He's also allergic to certain cleaning products, and he enjoys reading anything, even the terms and conditions on video games.
His dads always know when he needs to take a nap.
He is afraid of going to the dentist, to the point where he even scratched Harold when the latter tried to take him there. He is also apparently more energetic than both his dads, as when they tried to tire him out, it tired them out instead.