Packaged as the 'evil beast of a thousand bodies', upon his release Modulok was unique in form among the action figures. He is made up of 22 different pieces which can be locked together to form different shapes, in a Lego-like fashion. The character was conceived as a multi-bodied monster who can reform himself into thousands of different shapes to confuse his enemies. Among the fan community he is generally recognized as being a scientist, given that he is portrayed as such in the line's accompanying cartoon series. He is a member of the Evil Horde, though in some cartoon appearances is seen to work for himself. He is also known for creating Multi-Bot.
Modulok was introduced into the Masters of the Universe toy line in 1985, a little after the first wave of Evil Horde figures. His figure was an instant hit with buyers due to its unique nature. The figure came packaged in a cardboard case, its 22 pieces encased in a plastic bag within. These pieces include two heads and numerous arms, legs, torsos and tails which can lock together in seemingly endless ways. Some of the body parts are more human-like while others have claws and are more monstrous in appearance. There are even enough pieces to form two separate monsters.
The toy came packaged with the mini-comic "The Treachery of Modulok" which showcases the character and his abilities. He is introduced as a former slave of Skeletor who escape Skeletor's clutches and offers his services to the Evil Horde, knowing of Hordak's personal hatred of Skeletor. Together with Hordak, he proceeds to concoct a scheme involving his body parts being sent, one by one, to the Royal Palace of Eternia in separate cardboard boxes, labelled as presents to the members of the Heroic Warriors. Confused by the numerous body parts being delivered to the palace, Man-At-Arms suspects the forces of evil may be behind it and sends Prince Adam and Teela to Castle Grayskull with the body parts to ask The Sorceress about the creature. As they speak to The Sorceress, she informs them of the identity of Modulok, Modulok reforms himself and uses his shape-changing abilities to steal a forbidden weapon from the Castle. A battle then ensues involving a clash between He-Man, Skeletor and Hordak, in which Modulok showcases his shape-changing abilities, including his ability to split into two separate beings.
A later appearance in the mini-comic "The Menace of Multi-Bot" showcases Modulok as a scientist, tying in with his role in the cartoon series.
Several adjustments were made to Modulok's character by Filmation's writers and animators. Given Filmation's limited budget, Modulok would be a serious challenge for them to animate, given that his constant shape-changing would require the production of an exorbitant number of cel sheets for the character and therefore prove extremely costly. The decision was made, therefore, to simplify Modulok's design and give him one single shape to be used throughout the series. Although initially described in the scripts as appearing two-headed and multi-bodied like the toy, he appears in the cartoon with only one shape, his body appearing to be an organic whole rather than separate pieces locked together. He is also given only one head even though all of Mattel's promotional material depicts him with two. Possibly this may have been done to avoid confusion with Two-Bad, another two-headed character who debuted in the toy line and series at the same time. Another reason may have been for the purpose of making the character's design symmetrical, so that cel sheets could be flipped over without altering the character's appearance.
Introduced in the episode "Mistaken Identity", Modulok's character is also adjusted from Mattel's concept. His personality in the mini-comics is that of a rather generic villain, so Filmation expanded his character by making him a mad scientist hell-bent on proving his scientific genius. His debut episode was scripted by J. Michael Straczynski, who liked the character and went on to write most of his major episodes. A hardcore Star Trek fan, Straczynski based the character's personality loosely around Mr. Spock, feeling Modulok's pointy ears gave him a slight resemblance to the character. "Mistaken Identity" showcases him as the main villain. He begins as a deranged human scientist called Galen Nycroft, imprisoned in the Royal dungeons for attempting to use his science to control all of Eternia with a mind ray. Appearing human other than his deformed, enlarged eye which resembles that of Modulok, Nycroft is unfazed by the prison guards' mockery of him and vows to escape and prove himself.
He summons a bat-like aid to his side with a component needed to teleport his final invention to the prison cell. Teleporting the large machine to the cell, he steps inside, and an explosion comes from within. He steps out in the mutated form of Modulok, and uses his greatly bolstered strength to break free from the prison cell. He contacts Skeletor and offers him his services, but Skeletor rejects him describing him as a "wimp scientist" and vows to only accept Modulok into his evil crew once he has proven himself. Modulok sets out to prove himself by capturing He-Man. He fails in his scheme, as he is deceived into capturing a teenage boy who is trying to impress his girlfriend by pretending to be He-Man's secret identity.
He makes his second appearance in the episode "Happy Birthday Roboto", written by Larry DiTillio, which presents him as a solo villain, and also states that he is the sworn enemy of Man-At-Arms even though no other episodes touch upon a rivalry between the two. Cast in the role of main villain once more, this episode features Modulok capturing the heroic character Roboto and reprogramming him, then reviving him to carry out his own evil deeds. He proceeds to attempt a Frankenstein-like experiment on Man-At-Arms, intending to transfer his brain power into his second head so that he can possess Man-At-Arms' scientific knowledge for himself. This episode ties the cartoon version of Modulok in with the toy by alluding to his shape-changing powers and showing his extra head, although to save animation costs he did not put it on. The second head also seems to be cybernetic rather than organic as conceived by Mattel.
A third appearance on the He-Man series, in the episode "Here, There, Skeletors Everywhere" shows Modulok in the background among Skeletor's minions, indicating that he had somehow managed to gain acceptance into Skeletor's forces. Given that this is merely a non-speaking background appearance it is not explained how or when his services had been accepted by Skeletor.
Straczysnki continues Modulok's story with a brief cameo in the episode "Enemy With My Face" in which he is briefly seen attempting to regain Hordak's approval in order to become Horde scientist again rather than Horde cook. Although we never see him win this position back, he is seen back in the role of Horde scientist in the episode "Just Like Me" in which he is once again the lead villain, commanding an army of Horde Troopers in an attack on a peasant village. This episode also showcases a new power for Modulok: the ability to magically transform his arms into weapons, in this case a weapon resembling a lightsaber. This alternate kind of shape-shifting is perhaps a loose attempt to tie him in with the toy. Scripted by Gene Ayers, this is his only episode with a starring role not to be written by either Straczynski or DiTillio.
His next appearance is in DiTillio's "Black Snow" in which, in the role of sole villain once again, he leads an attack on Frosta's kingdom in order to stir up war between two tribes of the icy regions of Etheria. This episode once again showcases his ability to change his arms into weapons, in this case turning his arm into a cannon, much like Hordak does regularly in the series. The episode also showcases the character of Multi-Bot, Modulok's robotic assistant.
Straczynski used Modulok once more for his penultimate appearance in the episode "Darksmoke and Fire" in which he invents a rocket that sends She-Ra back in time, but this is only a cameo appearance giving little development to his character. Modulok's final appearance is in He-Man and She-Ra: A Christmas Special where he briefly appears as one of the warriors who accompanies Hordak when kidnapping children. After season 1, both Stracysnki and DiTillio left Filmation, and with Modulok's major writers no longer part of the crew, the character vanished completely from season 2.
Modulok is unique among all characters in the He-Man and She-Ra cartoon series, for having his own individual storyline throughout the episodes as well as being portrayed with more character depth than many other villains, rendering him one of the more memorable of all the less frequently-featured characters of the shows.
He also appears in the MOTU Marvel comics in the US, but his portrayal in these is very different from any other media. Whereas he had always been seen to possess only one mind, despite his two heads, this comic series portrays him with two minds, similar to Two-Bad, and much like the latter character, his heads would frequently argue with one another.