The character known as Doctor is a Decepticon who appears in the 2009 film Transformers: Revenge of the Fallen. His actual name is Scalpel, but he is exclusively referred to as the Doctor on screen. Physically, he is exceptionally small even by human standards, a stark contrast to most other Transformers. His alternate mode is a piece of scientific equipment: a lensmeter, a device used by optometrists, though his toy version transforms into a dissecting microscope. In his robot form, he has a vaguely insectoid appearance with six legs, two translucent arms, and large, inquisitive eyes that give him a deceptively harmless look.

In terms of personality, Doctor is defined by a chilling contradiction between his small, almost cute appearance and his profoundly cruel and sadistic nature. He speaks with a Germanic accent which, combined with his monocle-like eyes and clinical demeanor, gives him the air of a stereotypical mad scientist. He is the Decepticons' field medic and possesses vast databases of anatomical and mechanical knowledge, making him intimately familiar with most species in the galaxy. However, his approach to medicine is brutal and oriented more toward disassembly than healing. While he is extremely adept at taking things apart, he is known for having spare parts left over when he tries to reassemble them, leading most Decepticons to be reluctant to receive his care. He is driven by a clinical curiosity and a desire to extract information, regardless of the pain or harm he causes his subjects.

Doctor's primary role in the story is that of a surgeon and interrogator for the Decepticons. He is first summoned by Ravage and the Constructicons to the Laurentian Abyss, the underwater grave of Megatron. After a cursory examination, he diagnoses that Megatron requires spare parts and coldly orders the death of the smallest Constructicon, Scrapmetal, to provide them. Using those parts and an AllSpark shard, Doctor successfully rebuilds and revives Megatron into a more powerful form.

Later, Doctor is tasked by Megatron with extracting the Cybertronian symbols from the mind of the human Sam Witwicky. At a factory, he uses several invasive techniques on Sam, including sending a probe-like assistant into him, to confirm that the information is present. His chosen solution is to remove Sam's brain and place it on a table for examination. He prepares a buzzsaw to carry out this order but is interrupted by the arrival of Optimus Prime and Bumblebee, who rescue Sam. Though his fate is not shown on screen in the film, novel and comic adaptations depict him being destroyed by Optimus Prime.

Doctor's key relationships are defined by his function. He serves Megatons directly, acting as a subordinate who carries out his leader's orders for repairs and interrogation. Other Decepticons view him with a mixture of reliance and fear due to his dangerous and unfeeling methods. His relationship with his subjects, whether Autobot or human, is purely clinical and predatory, seeing them as specimens to be examined and disassembled.

Notable abilities include his vast scientific and medical knowledge, which allows him to repair and modify Cybertronian physiology. He is equipped with a number of surgical tools for his work, including scalpels and a buzzsaw. He also appears to be able to deploy smaller, probe-like assistants to enter and examine a subject's body from the inside. Despite his small size, his intelligence and expertise make him a uniquely dangerous figure among the Decepticon ranks.