Dr. Finkelstein is a resident of Halloween Town who appears in Kingdom Hearts, Kingdom Hearts: Chain of Memories, Kingdom Hearts II, and Kingdom Hearts 358/2 Days. His appearance is based on Tim Burton's The Nightmare Before Christmas. Portrayed as a mad scientist, Dr. Finkelstein performs experiments in his laboratory mainly trying to create life. He created Sally, a living doll who became his assistant. Confined to a wheelchair, Finkelstein has trouble getting around. He wears a helmet which can access his brain which he scratches thoughtfully at times. He can be grouchy at times, and is initially too busy in his experiments to develop friendships—although Jack Skellington seems to have succeeded. At times he can be kind, but this is rarely seen. He reprises a minor role in Kingdom Hearts 358/2 Days, alongside Jack and Zero.
 Kingdom Hearts
Dr. Finkelstein has a minor role in Kingdom Hearts. He is helping Jack create a heart, but it is stolen by Lock, Shock, and Barrel. The heart is retrieved by Jack, Sora, Donald, and Goofy, but only after Oogie Boogie swallows it to try and control the Heartless himself.
 Kingdom Hearts: Chain of Memories
Dr. Finkelstein makes an appearance as a figment of Sora's memory in Kingdom Hearts: Chain of Memories. In the game, Jack Skellington, requests that he makes a memory potion, hoping that it would help in teaching the Heartless new Halloween tricks.
 Kingdom Hearts 358/2 Days
Dr. Finkelstein appears once again in Kingdom Hearts 358/2 Days, helping Jack with his new ideas for Halloween. He is seen in the Town Square with the Pumpkin King on Roxas's second visit to Halloween Town, examining Jack's Heartless-filled balloons.
 Kingdom Hearts II
In Sora's first visit, Dr. Finkelstein is first seen looking at his book on constructing a robotic creature. When Jack arrives and ask him on the whereabouts on Sally is, Finkelstein tells him he was busy working on the experiment with the help of Lock, Shock, and Barrel. Eventually, however, their mischievous ways are annoying him as the trio soon tossed the robot arm on the table causing it to explode, and angrily called them "imbeciles".
Prior to Sora's second visit, Finkelstein has finished his experiment and tries to bring it to life but doesn't work. Realizing that their is nothing wrong with his design, along with Lock, Shock, and Barrel continuously dropping the parts they are meant to bring him, Finkelstein believes the Experiment to be a failure and decides to find "better assistants". However, just as he turns around to start new designs, the creation comes to life and attacks the doctor, leaving him unconscious in his laboratory. After regaining conscious, Dr. Finkelstein pleads for help that his experiment is missing. When he tells Jack and friends the full story Sora believes the Heartless might have taken the experiment, in which Finkelstein tells him that it was nothing like a Heartless. After defeating the Experiment, they return back to Halloween Town and tell the doctor that the experiment wasn't stolen, much to his surprise, and concluding it was an "overwhelming success". Sora then says that Santa Claus theorizes that the machine left, because it was probably looking for a heart, in which Dr. Finkelstein agrees, stating that he did not give the creature a heart of its own, as he did with Sally, and returns back into his lab.
Sometime after Xemnas's defeat, Dr. Finkelstein along with everyone else in the lab listen to Jack discussing plans for next Halloween.
Dr. Finkelstein is a frail-looking person, with thin, spindly limbs and very small hands and feet, but a disproportionately large head. He is confined to a black, electric wheelchair that seems to be rather old and difficult to operate. The chair is almost entirely metal and lacks any sort of cushioning, and it sports two levers, one on either arm rest, that Finkelstein uses to move it. Finkelstein himself dresses in a white lab coat that buttons up on the right side, pants of the same color, black shoes, and black gloves that are a good deal wider than his arms. His skin is an unhealthy white color and he has small, beady black eyes, normally covered by his goggles, as well as thin black eyebrows. His mouth is beak-like in structure and he seems to be missing a few teeth. Finkelstein's ears and nose are so small as to be almost nonexistent, and his nostrils point forward. Easily, Dr. Finkelstein's most prominent feature in his skull, which bears several obvious bolts and a clear horizontal seam going around the middle. Finkelstein can literally flip his skull open via a hinge in the back, exposing his pink brain, which he often scratches when attempting to figure something out.
The doctor is an extremely irritable, grouchy old man. He has a passion for inventing, though showing no skill at inventing whatsoever, shown by the following things: Sally was obviously not supposed to be a "good for nothing girl," and the heart, the potion, and the experiment all turned out wrong. In addition, he has somewhat of an ego, repeatedly insisting that his designs and inventions are flawless and finding ways to blame his failures on others, such as a shortage of ingredients for the artificial heart or a need of better assistants to construct The Experiment.
In Tim Burton's classic film, Dr. Finkelstein is the same character portrayed in the Kingdom Hearts series. As the creator of Sally, the doctor is exasperated and extremely irritated as Sally spikes his food and puts him to sleep while she ventures out. He usually tracks her down and returns her to the laboratory, locking her in her room. After Jack returns from Christmas Town, Dr. Finkelstein helps him perform some experiments to explain the meaning of Christmas. When Jack decides to run Christmas, he asks Dr. Finkelstein to create reindeer for a sleigh. He does, however, creating skeletal versions of it. Finkelstein spends the remainder of the film building a new assistant, who becomes a female version of him.