Though designing the dwarfs was relatively easy, animating them proved to be difficult, as the animators, already finding human figures difficult to animate, now had to animate 'ill-formed' human figures. Vladimir Tytla noted that the dwarfs should walk with a swing to their hips, and Fred Moore commented that the dwarfs had to move a little more quickly to keep up with the human characters. In order to establish Sleepy's character during the march home in "Heigh Ho", George Stalling noted traits specific to the character, to be taken into account in the animation: A drawing by Albert Hurter of Sleepy with his mouth wide open in a yawn inspired animator Fred Moore to be more extreme in Sleepy's animation. Moore made sure that, on every animation drawing of Sleepy, one eye was larger than the other, or one eye was more squashed than the other, to suggest the dwarf's perpetual weariness.
At a story meeting of October 3, 1934, the suggestion was made that Sleepy bring an end to the conflict between the fly and himself by trapping the fly in Snow White's glass coffin.
True to his name, Sleepy is always weary, droopy-eyed, and is always eager to fall asleep. Most of the scenes featuring Sleepy showcases the drowsy dwarf struggling to keep awake in the midst of a colorful event taking place.
Though usually stricken with laziness, he is a hard worker, but also a bit of a bumbler, as he often finds himself falling into accidental physical harm due to his lack of quick motion, such as whacking a deer's hide trying to catch a fly, or smacking himself with a cymbal doing the same.
However, in spite of spending most of his time nearly falling asleep, Sleepy is apparently the most observant and logical of the seven dwarfs, whether he knows it or not. He was the only dwarf to make the assumption that the Evil Queen may be attacking Snow White at the cottage when the forest animals frantically interrupted the dwarfs' mine work.
Sleepy is first introduced, with his six companions, at the Dwarfs' Mine. He controls the mine cart, presumably transporting the diamonds to Doc, who then sorts them. The cart is pulled by a deer. At one point the fly pesters Sleepy, who in an attempt to swat it accidentally hits the deer's backside; this causes the deer to kick the cart several times, sending Sleepy flying. As the dwarfs march home, singing "Heigh-Ho", Sleepy is fourth in line. He is the only other dwarf beside Dopey not to join in the singing, as he is too tired.
When the seven dwarfs reach their cottage, they think that a monster has taken up residence in their house. They sneak into the cottage (Dopey peeking through Sleepy's beard) and search the room. The dwarfs note that the cottage has been cleaned. They decide that whatever is in the cottage is upstairs, and Doc declares that one of them must go upstairs to chase it out of the house. Dopey is elected, and Doc, his hand shaking, gives Dopey the candle. Dopey is so terrified upon entering the bedroom that, when he hears a noise coming from the beds, he screams and rushes downstairs. The other dwarfs think that he is the monster and rush outside, locking the door. Dopey falls into the kitchen and emerges from the cottage, covered in pots and pans. When the other dwarfs see him they, thinking that he is the monster, start hitting him. When they realize that it is Dopey, they decide to venture into the bedroom. They are about to strike whatever is sleeping in their beds when they realize that it is the princess, Snow White. Grumpy begins to complain, and Doc attempts to silence him, but Snow White is woken up. She manages to match the name at the foot of each bed to the correct dwarf, identifying Sleepy third.
Eventually, it is agreed that Snow White will clean and cook for the dwarfs if she is allowed to stay. She prepares soup for them but demands that they wash first. The dwarfs reluctantly march outside. Here, the dwarfs, led by Doc, when Sneezy dips his finger in the water, he blubbers shocking Sleepy and the other dwarfs except for Grumpy, wash themselves, while singing "Bluddle-Uddle-Um-Dum (The Dwarfs' Washing Song)". Next to Sleepy, the fly can be seen washing on the soap. Grumpy refuses to wash, but the other dwarfs, led by Doc, to drag him to the water and wash him thoroughly. Later that evening, after supper, the seven dwarfs entertain Snow White with "The Silly Song"; to begin with, Sleepy is once again bothered by the Fly, and attempts to hit it with a cymbal, succeeding only in striking himself in the process. After they finish the song, the dwarfs listen to Snow White sing "Some Day My Prince Will Come", which sends every dwarf, except the stubborn Grumpy, into a dream-like state. Doc declares that Snow White will sleep in the bedroom upstairs, and the dwarfs must sleep downstairs. As Sleepy settles down next to the fireplace, where Grumpy is sleeping in the kettle, the fly sleeps on his nose.
The next morning, as each dwarf leaves, he is kissed by Snow White. While the dwarfs head to the mine, the Queen, as the Witch, makes her way to the cottage, knowing that only Snow White will be at home. Upon her arrival at the cottage, the animals sense danger and, after attempting to drive her away, rush to the mine to fetch the dwarfs, where they try to warn them. When Sleepy suggests that the Queen has found Snow White, the dwarfs rush home to find that the Witch has succeeded in poisoning the princess and is about to leave. The dwarfs chase the Witch into the mountains, and she reaches a cliff. She attempts to crush the dwarfs with a boulder, but a flash of lightning causes her to fall from the cliff and be crushed by the boulder herself.
The seven dwarfs mourn Snow White's death; Sleepy is shown silently weeping with Bashful and Sneezy. The dwarfs find her to be so beautiful, even in death, that they fashion a coffin from glass and place her inside. The Prince arrives, and the dwarfs part so that he can approach Snow White. He kisses her, breaking the spell of the Sleeping Death, and the dwarfs cheer. Before Snow White leaves with the Prince, she kisses each dwarf on the forehead (Sleepy was never shown being kissed on the forehead, but possibly was last).
In 1943's educational short, Sleepy and the dwarfs are enlisted in helping rid their forest and cottage home of deadly mosquitoes that can spread the harmful disease malaria. Throughout the animated short, the dwarfs give examples of the precautions necessary to keep people safe from the spreading crises and ensure safety.
Sleepy serves as one of the main protagonists in the animated series. He's often seen sleeping on the job and doesn't do much to further the plot of the story, in most cases. He also speaks with a droll, mellow tone. He has a tendency to sleepwalk or sleep-work.
The episode "Sleepytime" revolves around the weary dwarf. Here, the wicked witch Hildy Gloom casts a spell on the kingdom, putting all inhabitants into a deep sleep. That is, except for Sleepy and Sir Yipsalot, the pet pooch of Queen Delightful (the ruler of the Jollywood kingdom). Together, Sleepy and Yipsalot manage to sneak into the lair of the Glooms, learning the secret to breaking the spell, and venturing off to do just that before dusk; the spell's deadline. After successfully saving the kingdom, Sleepy is rewarded with a special trophy by the Queen, and deemed a hero by his brothers, whom he used as inspiration to assist himself throughout his journey.
Sleepy made an appearance in the episode "Wish Upon a Coin". He and the other dwarfs are first seen depositing coins into a wishing well, which are soon stolen by Pete, causing Sleepy and the other dwarfs to fall into panic. Mickey Mouse heads after Pete and manages to retrieve the coins, settling Sleepy and the other dwarfs and fulfilling their wishes (which is revealed to be a wish to have a head of hair). At one point, following the coin theft, Minnie Mouse tripped over a resting Sleepy during her pursuit of Pete.
Sleepy appeared in the 1941 wartime short, Seven Wise Dwarfs, in which he and the other dwarfs invest the proceeds of their diamond mine into Canadian War Bonds.
Sleepy is a member of the War Council and was seen aside Grumpy guarding Snow White's castle in "Pilot". In Storybrooke, he is Walter, a security guard who works at Storybrooke Hospital and occasionally dozes off on the job. He is also the Dwarfs Designated Driver and he falls asleep during that too. A night after a dinner party, Walter drives down a road as Leroy sits beside him in the front passenger seat. Leroy warns him to be careful steering the car. Annoyed, Walter reminds him that he's the designated driver, so he'll drive as he likes. After a moment passes, Walter unexpectedly falls asleep at the wheel. Shocked, Leroy attempts to regain control of the swerving vehicle. Up ahead on the road, the car nearly collides into a woman, but she freezes the entire van into ice which was created by Elsa
Sleepy, along with other dwarfs and Snow White, appears in their homeworld, Dwarf Woodlands.
Sleepy appears along with the other Dwarfs in the series, where their first appearance was in a glass podium with Snow White during the first game's Dive to the Heart. Unlike the Beast's servants, they are depicted as awake, meaning either their homeworld was not devoured by the Heartless, or that the Dwarfs were able to get to safety beforehand. Prior to the events of Kingdom Hearts, the Dwarfs' appearances in Birth by Sleep reveals their lives working in the mines for jewels until the arrival of the Keyblade wielders in their world. The Dwarfs encounter the first of these warriors, Ventus, and all show hostility towards the newcomer, with the exception of Dopey. After returning to their cottage, the dwarfs meet Snow White for the first time and take her in after she claimed she was attacked by an Unversed. Unfortunately, Snow White falls into a deep slumber after taking a bite from the Queen's poisoned apple and the Dwarfs place her in a glass coffin to mourn her. Sleepy laments how much he'll miss Snow White's bedtime stories. However, thanks to assistance from Aqua and the Prince, Snow White is able to awaken, and the Dwarfs celebrate. (Like the film, Sleepy was never shown being kissed on the forehead by Snow White, but possibly was last).
Sleepy also appears in Kingdom Hearts χ along with the others in Dwarf Woodlands.
Sleepy is a rare character when it comes to meet-and-greet sessions, but even so, he and the other dwarfs are commonly utilized in the Disney theme parks around the world. He wears an amber outfit with a fuchsia hat, green pants and orange shoes.
He is revealed to have a son in Descendants, on the School of Secrets videos (#3). His son is not named, but the same actor does briefly appear in the film during the "Be Our Guest" number for Family Day. His son has curly red hair and glasses.