Casey is a 2-4-0 steam tender locomotive with a small, four-wheeled tender at the back, a big, tall smokestack, a small headlamp in a baseball cap-shaped casing, a tall steam dome with a whistle on top, and a small cowcatcher on his front.
Casey is a 2-4-0 steam tender locomotive hauling the WDP Circus train, and he even has his own theme song. He appears frequently throughout the film, and is shown to be somewhat sapient. For example, when the Ringmaster calls, "All aboard! All aboard!", his whistle can be heard calling, "All aboard! Let's go!"
As is the case with most Disney vehicles, Casey has the ability to move more fluidly than real life locomotives, and his boiler is often seen bending and twisting like rubber when in motion.
In addition, Casey can twist and flex his metal body to express motion. He uses his steam cylinders like limbs, giving him the ability to shrug, point and make other gestures.
While the sound of the voice resembles that of one processed through a vocoder, it was actually done with a more primitive device, a Sonovox, which uses one or two small loudspeakers in contact with the throat, which allowed Wright to "speak" by modulating an artificially produced sound with her mouth.
In earlier work, according to a deleted scene from Dumbo, Casey was, in fact, pulling a passenger train to Cleveland, Ohio. At one point during the excursion, he gets into conflict with a steamboat over the right of way on a drawbridge that spans the river, before overcoming him and causing the drawbridge to close on and push down on the steamboat into the water. Later on, Casey encounters a streamlined train charging towards him and closing in fast, at which he desperately called for a nearby railroad switch lever to wake up and change the track, which it did. He thereafter crashes after an effort to jump the chasm left by a broken bridge in a storm.
In this film, his coupling rods were connected to his foremost driving axle. He also had a roof-mounted bell and was not as stubby. When he was hired for the circus train, he had a few changes: his coupling rods were extended and moved to his rear driving wheels, his bell was removed, and he became stubbier. This implies that he was overhauled after the accident and bought by a railroad based in Florida that served the southeastern United States.
A Disneyland attraction named the Casey Jr. Circus Train is based on Casey, with an updated version running at Disneyland Paris. Casey Jr. Splash & Soak Station, a water play area themed around him, was added to the Magic Kingdom in 2012 in the Storybook Circus section of that park's new Fantasyland. He is also the second float in the Main Street Electrical Parade, driven by Goofy and pulling a drum with the parade's name and logo; when the parade returned to Disneyland in 2017, he was made the lead float.
- Casey makes a cameo in the Donald Duck cartoon Spare the Rod as a silhouetted train crossing a bridge.
- Casey is the second float in the Main Street Electrical Parade and its versions. He, driven by Goofy, pulls a drum with the parade logo, along with Mickey Mouse and Minnie Mouse.
- Casey makes a brief cameo in the 1988 film Who Framed Roger Rabbit. He is spotted during the final scene.
- The wagons that transport P.T. Flea's Circus in A Bug's Life are old boxes of Casey Jr. cookies.
- In Kronk's New Groove, the sequel to The Emperor's New Groove, Kronk has a miniature model train set of Casey in his new home, complete with scaled-down models of the carriages featured in Dumbo.
- Casey was named after John Luther "Casey" Jones, an engineer from the late 1800s who was famous for driving trains at great speeds (sometimes dangerous speeds) in order keep on schedule.
- In the film, Casey does not appear to have an engineer in his cab, so it is unknown how he is able to move on his own in the first place, unless he is a sentient being.
- Casey makes a cameo in the Mickey Mouse episode "Tokyo Go". In the episode, Casey appears as a miniature train piloted by Mickey Mouse as a children's attraction, in reference to Walt Disney's backyard Carolwood Pacific Railroad, complete with Walt's barn (a photo of Walt in the cab of Disneyland Railroad locomotive E. P. Ripley also appears in the scene).
- When Casey climbs up the mountain, he chants, "I think I can," over and over again, and on the way down he chants repeatedly, "I thought I could." This is a direct reference to the classic children's book The Little Engine That Could, in which the titular anthropomorphic locomotive chants these same words. In addition, Casey's cab and firebox have their colors inverted.
- The "Casey Junior" segment was originally much longer. It was drawn and animated, then heavily edited, cutting several minutes from its run time. The full length segment can be seen on Disney's The Reluctant Dragon DVD.
- Casey's train, for some reason, seems to be constantly gaining and losing cars as he makes his journey; the only time he is ever seen with all of his cars intact is when he crosses a bridge before climbing up the mountain.
- The train Casey pulls in the film, from front to back, is made up of a yellow coach (carrying the clowns and other circus performers), a flatcar with a calliope organ and a various circus wagon, another flatcar (carrying two other various circus wagons), an orange stock car (carrying the elephants), a blue stock car (carrying animals like monkeys, horses, zebras, and camels), another flatcar (carrying the tent and its supports), a light blue stock car (carrying the giraffes [whose heads are clearly sticking through the roof]), one more flatcar (carrying two more wagons), a pink stock car (carrying predators like hyenas, apes, bears, lions, and tigers), a light green stock (carrying animals like ostriches, seals, hippos and kangaroos), a green coach (carrying the circus workmen), and a red caboose numbered 2 (carrying the ringmaster). Also, at the end of the film, the caboose is replaced with a silver coach reserved for Dumbo and Mrs. Jumbo.
- Casey makes a brief cameo in Where's My Mickey?.
- In Dumbo, Casey is a 2-4-0 steam locomotive, most likely to be of an American design, and numbered "8" on the Illinois Central Railroad and "1" on his own railroad, but in real life, a Baldwin steam locomotive and numbered unknown variously on the Illinois Central Railroad and an unidentified number of other railroads.
- As a matter of fact, animator Ward Kimball owned an 1881 Baldwin Mogul 2-6-0 steam locomotive, which he ran on the Grizzly Flats Railroad. Casey is based on that particular locomotive.
- Casey's sound was reused for the dishes from The Sword in the Stone, during which Sir Ector pushes the dishes aside violently.
- Casey makes a cameo at the beginning of the 2016 live-action Jungle Book remake during the film's opening Disney logo (re-created using traditional animation instead of CGI, thus replacing the realistic train from the original version of the current logo), where he is seen as a silhouetted train crossing a trestle over a river behind an amusement park just right before the castle is shown.
- Casey strongly resembles a locomotive that was built by Baldwin Locomotive Works in 1900 for the Old Sydney Colliery Company. This locomotive (numbered 25) worked at the Sydney, Nota-Scotia colliery until the early 1960s. It is currently on display at Delson, Quebec, Canada today.