Emergency Medical Holographic program

The Emergency Medical Holographic program (EMH) was a sophisticated hologram used on most Federation starships in the late 24th century that was designed to provide assistance to medical staff in times of emergency. It was developed by Dr. Lewis Zimmerman on Jupiter Station and was formally known as EMH Program AK-1 Diagnostic and Surgical Subroutine Omega-323. 

Mark I
The Mark I was based on their designer, Dr. Zimmerman, both physically and psychologically. This produced an arrogant and irritable hologram that became notorious for its less than gracious bedside manner, which saw some doctors try to avoid activating the program. 

The first vessel equipped with the Mark I was the USS Voyager (NCC-74656). The Doctor, as it was known on Voyager would also become the most notable Mark I due to its continuous operation over several years and it evolving from a purely short-term emergency protocol to a critical and important contributor to the crew of the USS Voyager during its years stranded in the Delta Quadrant. ()

The Mark I would eventually be declared "defective" and replaced by newer models. The Mark Is were transferred to undertake menial tasks such as dilithium mining and scrubbing plasma ducts. 

Mark II
The EMH Mark II was the designation for the second instalment of the Emergency Medical Holographic program, which became standard equipment aboard Federation starships starting in 2374. The Mark II prided itself as superior to its predecessor, the Mark I, whose appearance and personality were modeled after project designer Lewis Zimmerman. 

Although the EMH Mark II was programmed with a better bedside manner than the Mark I, USS chief medical officer Aurellan Markalis found that ship's Mark II to be just as rude as its predecessor. Its standard greeting to individuals with whom it was unfamiliar was "What the hell are you doing in my sickbay? I am programmed to identify every member of this crew. You are not one of them." As of the launching of the Lambda Paz, the program had not been updated to identify Limis Vircona and the other Maquis aboard as members of the crew, and so regarded the captain as an intruder when the two first met. (: "Revenge a Dish Best Served Cold")

Later versions
By 2376, a Mark III and Mark IV of the EMH program had been developed. Additionally work was started on a variant known as the Long-term Medical Holographic program. 

Zimmerman eventually developed a version with full medical capabilities and functionality based on The Doctor, known as the Supplementary Medical Holographic program. 

Mark V
As of the creation of the Mark V in 2381, the EMH had been renamed the EH or Emergency Hologram as of the inclusion of the hologram being able to act as a Medical Officer and a Command Officer after the return of the USS Voyager (NCC-74656) in 2378.

One major difference of the Mark Vs was their ability to be customly designed for each starship they were used on, allowing a Captain to decide upon their behavior and other important details to a limited degree that were not possible on the previous versions. (Star Trek: Future Perils)

Mark VI
In 2402 a new project was started entitled the Mark 6 Project. This was a project designed to create the Emergency Hologram Mark VI to enable it to be an effective member of the crew. In addition because holograms now had free reign to explore starships and could even leave said ships if the place they went to had holographic technology it was decided the project should be started.

A key difference between the Mark V and the Mark VI was the ability for expanded role additions, in particular the main roles being a Doctor, an Engineer, and a member of the Command staff which in the most dire case would be acting Captain. One of the unique abilities per say for the Mark VI was for the uniform colour to change depending on the location on the ship the hologram was called to, something the Mark V couldn't always do. The previous limitation of customization was also increased. The prototype model was installed on the USS Pureshasu (NCC-86521). (Star Trek: Future Perils)

Other races
Romulans designed an EMH based on a design of holo-emitter that was extensively used by the Tal Shiar to execute missions that required shapeshifting. As such, the EMH could change its appearance according to the patients it served.

Sometimes, faulty EMHs could be frightening to behold by Romulans. Depending on the nature of the EMH's failure, they can frighten patients rather than help them heal. Also, their holoprojector was located into their footwear, thus limiting their capabilities for shapeshifting. This could be a liability for the Tal Shiar if they chose to use EMHs on espionage missions among the Hydrans or other species that had abnormal feet, like Bowsers.

The Rakelli were also fond of using EMHs as fashion objects, but as a fashion object, it was more the shoe in which the holoprojector was placed that served as such, rather than the EMH itself, although EMHs were used on occasion by Rakelli fashion designers as models for clothing. Their EMHs had a changeable holoprojector.

Starfleet

 * USS Argus (NCC-75124)
 * Andy
 * USS Prometheus (NX-59650)
 * Lou
 * USS Pureshasu (NCC-86521)
 * Kazue
 * USS Voyager (NCC-74656)
 * The Doctor

RIS

 * Since the crewmen on the Bouteina has changed the appearance of their EMHs several times, and they even had more than one, the personalities of these EMHs are listed in chronological order by their owners.


 * Pazzo (Mark V EMH)
 * Unnamed Human ("Marianela (RIS Bouteina episode)")
 * Unnamed Hydran ("Monster-in-a-Box")
 * Myriam Gency ("Miracle in Whoville"; later transferred to Rihanna)
 * Pazzo (Mark VI EMH)
 * Bouteina ("Days of Wine and D'ohses")
 * Rakelli
 * Unnamed Rakelli ("Yesterday's Lyrans")
 * Marina Mur'Eq ("Hussade Contract")
 * Rihanna (Romulan)
 * Myriam Gency ("Days of Wine and D'ohses")
 * Florina ("Doctor Rihanna")

Ships with unnamed EMHs

 * USS Artemis (NCC-75128)
 * USS Bluefin (NCC-4458)
 * USS Cantabrian (NCC-24705)
 * USS Invictus (NX-90585)
 * USS Vitality (NCC-95238-P)
 * USS Voyeur (NCC-76450)

Background Information

 * The EMH-Mark I was played by.
 * The EMH-Mark II was played by in.