Arliss Coates is the tritagonist, Jim and Katie's younger son, and Travis' brother in Old Yeller and its sequel, Savage Sam. He is a curious little boy who adores Old Yeller from the beginning, as he feels the need for a good hunting dog.
Arliss is seen to be a very curious child, asking all sorts of questions. But he also very stubborn as well, when Arliss wants to go with his father to Kansas and he says no Arliss puts up a really big fuss. He also doesn't like being bossed around (mainly by his older brother Travis Coates) even throws rocks at him whenever he gets really mad. But overall, Arliss is very kinds and very helpful.
Arliss is first seen along with his older brother Travis riding on their father's horse asking questions like what their father is going to sell their steers for? As he prepares to leave Arliss puts up a big fuss, wanting to go with him but his father tells him that he needs to stay and take care of his Mama.
Arliss is seen again later on in the evening, coming home from "Bear Hunting" and asks who busted down the fence? When Travis says that it was a stray dog, Arliss states that he needs a good hunting dog, when his mom Katie tells him to go outside and wash up for supper.
The next morning Arliss awakes to find Old Yeller outside and immediately claims him as his dog. When he sees Travis angrily grab a stick, Alriss grabs one too and the two engage in a stick fight when their mom comes out and breaks it up. Upon seeing how Arliss has already bonded with the dog allows him to keep him and the two begin playing with each other. Later on when Travis finds the two splashing around in their drinking water and tells them to get out, Alriss just sticks out his tongue and refuses to listen to him. Before long the two brothers engage in another fight, as Arliss begins throwing rocks at his brother until their mother breaks it up once more and tells Arliss that needs to start minding his big brother and sends him inside to change out of his wet clothes.
The very next day, while Travis and Katie are cutting fence posts Arliss and Old Yeller are by the creek about to catch a catfish. After successfully doing so, Arliss presents the fish to his mother and tells her tall tale about how he had dive deep under water to catch it. Of course neither she nor Travis believe him, but humor him anyway. Arliss then attempts to catch a black bear cub with a piece of cornbread, but once he gets ahold of the cub, Travis and Katie are alerted by the sound and see the cub's mother charging towards Arliss. They both rush in, while Old Yeller fights off the bear Katie grabs her youngest and retreats back to the house and cries tears of relief that he's safe and almost got himself killed and the whole family praises Old Yeller for his bravery
Sometime later, Arliss and Old Yeller are playing in the field when Travis shows up and asks Arliss to bring Old Yeller to the house. When Arliss sees Old Yeller's owner Burn Sanderson taking him away Arliss begins to throw a fit and throws rocks at him in anger. Mr. Sanderson then talks to Arliss and the two agree to trading Old Yeller for his horned toad and home cook meal and Alriss gets to keep Old Yeller.
The following day, after Travis and Old Yeller had gotten hog-cut Arliss accompanies his mom and brother as they go out to find Old Yeller. Katie sends Arliss out to catch a lizard they passed earlier, while she and Travis stitch up Old Yeller's injuries. When Arliss get back with the lizard, Katie has Arliss hold it for her until they get back home and has him lay with Old Yeller as they tow him back home.
Another day later, Bud Searcy and his daughter Lisbeth Searcy arrive with a puppy for Travis, but doesn't want it and suggests giving him to Arliss and the the two quickly bond and takes the pup everywhere. Late one evening Travis and Alriss hear their mother holler out in distress as a rabid wolf shows up, Travis orders Arliss to stay inside while he runs out and shoots the wolf. After Old Yeller gets pinned up after the fight with the wolf to see if he's got rabies or not Arliss wants to let his dog back out. So one evening after his mother tells Arliss to go to bed, Arliss sneaks over to the corn crib and attempt to let Old Yeller out, unaware that Old Yeller is rabid. Katie quickly sees Arliss trying to open the door and rushes over and shuts it and takes Arliss back inside.
The next day, when Jim returns home Arliss is the first to welcome him back. Jim presents him with an Indian Chief's head headwear and toy axe tool and then goes off with his puppy to play. At the end of the movie, Arliss and Travis are out with their puppy, now a full grown dog.
In the sequel, Alriss and Travis are left in charge of the farm while their parents are away visiting their ailing grandmother. Arliss is first seen coming out of his and Travis' room and sees Sam eating a side of meat that was hanging hanging from the door. Arliss tries to take it away from him, but Sam growls at him so Arliss lets him have it. Arliss then sees Jumper the mule eating the corn out of the field and is outraged and begins throwing rocks at him to get him out.
Inside the house, Arliss asks Travis how much longer their parents will be in San Antonio, thinking it'll be until their grandma dies. Arliss states that he'll never die, when Travis tells him to go out and milk the cow so he'll have something to live on. So Arliss goes out and milks the cow singing "Old Dan Tucker", during which the farmyard cats show up and Arliss begins squirting milk in their mouthes until Sam enters the pin and startles the cow, Travis overhears the chaos and calms things down. Travis then scolds Arliss, only to aggravate him and Arliss angrily begins throwing rocks at him. The boys uncle Beck Coates shows up and sees what's going on and asked Arliss what's got him so riled up? Arliss begins to explain how Travis is always bossing him around and never letting him have a say in anything. Beck then uses reverse phycology on Arliss and he goes back to milk the cow.
Later, while helping Travis clear the field of brush, Arliss sees Sam chasing a bobcat that's been raiding the chicken roost and wants to go get it. Travis states that they have to finish the work first and then they can go catch it, but Arliss states out loud that he'd rather chase a bobcat that work and mounts Old Jumper and rides off, much to Travis' objection.
Travis and Lisbeth soon find Arliss and Sam at the bobcat's den trying to catch it, after failing to get him to come out Arliss begins kickingTravis off. Travis having enough of Arliss' stubbornness angrily twists Arliss' foot and forces him out. Arliss now raging mad begins throwing rocks at Travis once more and a fight breaks out between the two brothers, shortly after Lisbeth tries to break it up a gang of Apaches appear and kidnap them.
After crossing a river, Arliss attempts to escape but the Indians catch him and begin tossing him around. Later when they break camp, Arliss suggests getting two of the Indians into a fight over who gets Lisbeth for a squaw so they can get away and bring back help, but Travis refuses to put her in danger. As evening falls the chief gives the three of them each a piece of horse meat to eat, after Arliss sees that Jumper is no where to be found he assumes the Indians butchered him and refuses to eat. After being convinced by Travis to eat, Arliss begins to think about how much help Jumper was to their family. Arliss then takes a large stick and walks up to one of the Apaches and knocks him out for assumingely butchering Jumper. The Indians admire Arliss' spirit and decide to make him one of them, they all pile on him and rip off his shirt and pants and paint marking on his face making him an Indian like them.