The Doctor, an Emergency Medical Hologram (EMH), is a fictional character portrayed by actor Robert Picardo in the television series Star Trek: Voyager, first aired on UPN between 1995 and 2001.

Despite Ethan Phillips' getting the part, Picardo was asked by the producers to come back and audition for The Doctor—something that shocked him, because usually actors would be passed over completely.

The Doctor begins his service on the USS Voyager as the standard Emergency Medical Hologram (EMH) built into almost every newer Starfleet ship's sickbay.

The EMH eventually develops his own personality, although he generally maintains his acerbic wit and irritating "version one" bedside manner.

As he was originally intended as a temporary medical backup system, not as a digital life form, Voyager's journey strains his programming to some limits.

Attempting to develop a realistic personality, the Doctor not only manufactures a holographic family ("Real Life"), he also has an increasing number of other "human" experiences.

When The Doctor later discovers clues as to what had happened, Captain Janeway is convinced by him and others that he has a right to learn to come to grips with the guilt in the manner of any other sentient being rather than be treated merely as a defective piece of equipment.

The Doctor submits a holonovel titled Photons Be Free to a publisher on Earth, detailing the manner in which holograms are sometimes treated by Starfleet.

Although he has previously been confined to Sickbay or the Holodeck, the mobile emitter allows The Doctor to move about freely, making him ideal for missions where the environment would be harmful or otherwise fatal to the crew.

In a 2020 interview, Picardo recalled his initial reticence to the concept of a mobile emitter: I remember I was in [Voyager producer] Brannon Braga's office when he told me.

In the following season episode "Workforce", the idea is realized when the crew is forced to abandon ship, and The Doctor takes over command functions.

The episode "Living Witness" depicts a future Delta Quadrant civilization building a museum around Voyager artifacts, including its redundant EMH photonic processor.

Before the arrival of the mobile emitter, The Doctor's holo-program was confined to sickbay, holodecks, and other areas equipped with holographic systems.

The Doctor is also able to download his program and personality subroutines into a humanoid with Borg implants, indirectly "possessing" that individual and gaining control over its "host" body.

The EMH is a holographic computer program designed to treat patients during emergency situations, or when the regular medical staff is unavailable or incapacitated.

EMHs are a standard feature onboard all Starfleet ships, but they are there only to supplement the living medical crew during emergencies, not replace it.

[5] Another author observed that consequent to the EMH's portrayal in Voyager, "sentient computer programs embodied in a computer-generated hologram became a commonplace idea – even a convention – in subsequent fiction".

[6] In a minor role in the movie Star Trek: First Contact, Picardo plays the emergency medical hologram of the USS Enterprise-E.

Doctor Beverly Crusher activates it/him, albeit reluctantly, as a means of distracting the Borg while she and other crew members escape from the besieged sickbay.

In 2019, Picardo said CBS producers had expressed interest in also having him in Star Trek: Picard as either The Doctor or his creator, Lewis Zimmerman.

Star Trek: Picard features an EMH called "Emil", part of a holographic suite aboard the ship La Sirena, modeled after Captain Cristobal Rios and played by Santiago Cabrera.