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Memory Alpha

The following is a list of Klingon calisthenics program holograms.

Feathered alien

A feathered opponent

This feathered ornithoid alien was a holographic opponent in Worf's Klingon calisthenics program on board the Enterprise-D. It was part of the program when K'Ehleyr ran it and attacked her twice. (TNG: "The Emissary")

This alien was played by an unknown stunt performer.

Insectoid alien

An insectoid opponent

Another insectoid opponent

This insectoid alien was a holographic opponent in the Klingon calisthenics program, created by Worf aboard the Enterprise-D.

When Commander William T. Riker accompanied Worf for the first time into this program, this opponent attacked Worf but was knocked down by Riker. (TNG: "Where Silence Has Lease")

It was also activated when Worf increased the program to level two in 2365 while he and K'Ehleyr used the program. (TNG: "The Emissary")

This opponent was played by stuntman Steve Kelso in "Where Silence Has Lease" and by an unknown stunt performer in "The Emissary".

Skull monster

The skull-faced alien was part of Worf's Klingon calisthenics program on board the USS Enterprise-D. (TNG: "The Emissary", "New Ground")

When Commander Riker accompanied Worf for the first time into this program, this skeletal opponent attacked Worf while Riker had to face the insectoid opponent. (TNG: "Where Silence Has Lease")

The same year this skull faced opponent also appeared in the program when K'Ehleyr used it. Worf defeated this opponent by cutting his upper part of the body. (TNG: "The Emissary")

Jadzia Dax kept a similar Klingon exercise program in the holosuites on Deep Space 9 that also featured this alien. In 2372 she surprised Worf, who used this program and Worf was surprised that Dax was the creator. (DS9: "The Way of the Warrior")

According to the script for "The Way of the Warrior", this was a "hulking ogre-like monster from Klingon mythology." [1]
According to the Star Trek Encyclopedia (4th ed., vol. 1, p. 113), the mask used was that "of the character Skeletor from the movie Masters of the Universe." Star Trek makeup designer Michael Westmore also did makeup work for that film. Star Trek: Deep Space Nine guest star Frank Langella played Skeletor in the film whereas Star Trek: Voyager star Robert Duncan McNeill played the role of Kevin Corrigan, and Meg Foster of Evil-Lyn.
The skull faced alien was played by stuntman Jan Shultz in "Where Silence Has Lease", Dennis Madalone in "New Ground", and Chris Doyle in "The Emissary". In Deep Space Nine, it was played by stunt coordinator Dennis Madalone, who took a hit in his eye while filming the fight scene with Michael Dorn, and stunt actor Tom Morga took over for him; neither received credit for their appearances. (Source: Tom Morga)