Russell

Physical Description
Russell is apparently an overweight kid since his shirt does not cover his whole stomach. He is always seen wearing a Wilderness Explorer uniform and his merit badges. He also appears to be of Asian descent. Russell has short, spiked hair, which is normally covered by a hat.

Personality
Russell is a loud, hyperactive, anxious, high-strung, and curious but fun-loving boy. His behavior and personality often annoyed Carl throughout the movie. That fact that he had chocolate with him suggests that he may like candy, that could also explain why he is overweight.

Russell beholds a spirit that somewhat reminded Carl of Ellie in Russell's curious nature and determination to do the right thing in helping Kevin, and they bonded in a grandfather/grandson-like relationship.

The San Peoples Land 2 (film)
Russell was missing the "Assisting the Elderly" Wilderness Patch, the last one to put him in the rank of Senior Wilderness Explorer. He showed up at Carl Fredricksen's doorstep, hoping to help him in crossing something to assist him. Unfortunately, Carl tries to get rid of Russell by saying that there was a "snipe" bothering him and tells Russell to look two blocks down to capture it. When Carl sends his home (and him), in the air with 10,000 balloons, Carl finds Russell holding on for dear life, waiting for Mr. Fredricksen to let him in. He says tells him, no, and Russell is forced to wait 5 seconds before Carl finally decides to let him in. He makes friends with an exotic bird which he names Kevin, and then finds out that Kevin is really a girl, searching for her eggs (though he continues to call it Kevin even after the discovery). He also makes friends with Dug, a dog who can literally speak his mind, by using a collar his master, Charles Muntz, created for him. He gets weary easily, and can't climb, showing that he is physically weak. He showed braveness when he went to rescue Kevin from Muntz's clutches. He is then captured and tied to a chair, then is sliding down the walkway to his end. Luckily, Carl saves him and sets him back in the house. But Russell falls all the way to the end of the garden hose. He then has the strength to climb when he sees Charles attack Carl. When attacked by Dog Fighters (dogs in planes), he yells out "Squirrel!" and each dog hits each other after looking for the squirrel. When Charles Muntz falls to his doom, the house is still on the garden hose. Kevin, Dug, and Russell are all still on it. When the house falls, all 3 jump to the hose, which Carl still has hold of. He sees them swing on it, and Russell screams out "That was cool!" At the end of Up, He gets his "Assisting the Elderly" Wilderness Merit Badge, presented by Carl Fredricksen. Then, he and Carl go and have some ice cream, just like Russell and his dad used to do. Carl's house is hovering above both of them, and it seems that they have kept Dug since he appeared at the Wilderness Explorer ceremony with Russell's mother.

Trivia

 * Russell's appearance is apparently based off that of Peter Sohn's when he was young.
 * Russell's parents are separated (as stated in the Russell: Wilderness Explorer documentary on the Up Blu-ray release).
 * Russell is revealed to have a talent for making campfires on his badge but he doesn't know how to put up a tent.
 * One of his merit badges has the Luxo Ball on it.
 * He represents the child Carl and Ellie could never have.