Scorponok is the Decepticon Headmaster leader and transforms into a scorpion. He is either the Nebulan leader Zarak bound to the head of a Decepticon, or in Japan, is a diminuitive Transformer bonded to a Transector. He is a minor antagonist in the US, but is the main antagonist of The Headmasters, and the tertiary antagonist of Super God Masterforce.
In the US
In the comics, Scorponok is bonded to the Nebulan leader Zarak, who attempted to rule both Cybertron and Nebulos, he is confronted a number of times by the Autobot Headmasters and is eventually defeated.
Scorponok appears in the finale to the US original show. He is shown to be highly malevolent, agreeing to aid the Decepticons in exchange for his minions being allowed to bond with the Decepticons. After retrieving the key, Scorponok departs and aids Galvatron against the remnants of Autobot resistance. He is able to convince the reluctant Galvatron to talk and shortly afterwards hands Galvatron the key to the plasma energy chamber, he battles Fortress Maximus, and is ultimately defeated and flees into space. Zarak then bickers with Galvatron and when Galvatron states he will rule the galaxy, Zarak simply states "We will see" hinting he intends to become Decepticon leader, though the series ends, leaving it up to debate.
Scorponok in the Headmasters is much more different than in the Rebirth. In Japan, he is a diminuitive Transformer who fled Cybertron to planet Master with several other Transformers. He eventually became involved in the Headmaster program, but disgruntled with Fortress's leadership, orchestrated a rebellion against him. Scorponok was banished, but made contact with Galvatron in 2011( as opposed to 2007 in the US) and joined forces. Scorponok's soldiers joined in several of Galvatron's schemes, but their master stayed in the shadows, supplying Galvatron with the technology to revieve Soundwave as SoundBlaster and also arranging for parts of his Transtector to be built on Planet Beast.
He eventually emerged to confront Fortress on planet Praum and attempted to drown them in sand. When they managed to get out, he fled and left his minons and Galvatron to be beaten by the furious Autobot Headmasters. He later questioned Galvatron about the need to seize the new alloy, to which Galvatron furiously voices his power. Sixshot later informs Scorponok that Galvatron will banish him once he has the new alloy and Scorponok, fearing for his life, has his soldiers plant bombs in Vector Sigma's chamber, which destroys Cybertron, the new alloy, and also presumably killing Galvatron, enabling him to seize leadership.
He then had the Decepticons move ahead with the construction of his Transtector by stealing a sateliite and powered it up with solar energy, alerting the Autobots to the construction facility. Scorponok then decides to force the Headmasters to focus on Earth as heavily as possible to keep them from uncovering the facility. A volcanic eruption he engineered through unknown means, succeeded and was able to delay survey of the facility. An attempt to use a giant plant was similarly successful, but he was shocked to see Fortress transform into a massive robot( his reaction indicates that he assumed that Fortress did not have a similar Transtector) and was forced to take this into consideration. He also became obsessed with the power of plasma energy unleashed in Cybertron's destruction.
Determined to gather more plasma energy to make the Decepticons more powerful, and deciding to defeat Fortress for good, Scorponok decided to blow up Mars. He engineered a plan to force Fortress to come to Mars in person and subsequently managed to succed when the plasma energy cancelled out Fortress's own energy. He then revealed his true form and merged with his Transtector in a spectacular ceremony, and went to Charr before heading to Mars. After easily crushing the Headmasters, he emerged into a giant robot form and began to pummel the helpless battleship. He eventually departed when Mars was blown up, but was aghast to learn that Fortress had assumed his giant form and cleaved his shoulder, and Scorponok was forced to retreat. Scorponok was nevertheless pleased, for despite his injury, Mars was destroyed and Scorponok's plan was successful.
Scorponok then attempted to declare himself emperor of the Decepticons, but when Galvatron returned, he was reduced to a insulting transport mode when Galvatron subsequently went on a planet hopping expedition for energon to fufill his master plan. On planet Darhos, Scorponok learned that the Beastformer Tekna, who had discovered the Transector's weak spot while working on it, was on the planet, having been imprisoned on Galvatron's orders and feared that he might give the secret to the Autobots anyway since the Autobots were hot on their heels. He inmediatly informed the Decepticon Headmasters to kill Tekna to ensure his weakness was kept a secret. Tekna was killed by Weirdwolf, presumably to Scorponok's relief, unaware that Tekna had given them encrypted microfilm that gave them the information.
Upon their return, Scorponok decided to seize leadership again, and planned to force Galvatron to fight the Autobots in person. Sixshot then informed Scorponok that Galvatron planned to incorporate Earth into his body and become antoher Unicron. Although Scorponok had already figured it out, Sixshot informed him that Galvatron would need parts from elite soldiers and Scorponok realized that his Transtector would be one of those elite soldiers. He revealed his knowledge of the plan, and a struggle with the Autobots ensued, during which Galvatron was killed and buried under the icebergs. Scorponok was forced to retreat, but happily took advantage to declare himself "Emperor of Terror" and inmediatly ordered the planting of bombs in areas of volcanic idea in an attempt to harness its plasma energy. Fortress arrived to confront him, but was unable to transform into robot form and Scorponok hurled into a volcano. This enabled Fortress to transform into his robot form by siphoning the energy form the lava. Scorponok probably would have won had Chromedone, who had just discovered that Scorponok's weakness was his Decepticon symbol on his chest, not arrived and revealed it. Aghast and horrified, Scorponok attempted to protect his chest, but Fortress plunged the Master Sword deep into the symbol. Critically wounded, and realizing he could not fight Fortress with his weakness revealed, Scorponok fled Earth with many soldiers of his army.
Scorponok then head to Master, his adopted homeworld, in an attempt to create a shield powerful enough to defeat the Master Sword. He kidnapped one of the scientists, but upon learning only Fortress knew of the secret, subsequently established an arms factory in an area rich in G metal. His Headmaster minions assumed that the metal would be an instant win against Fortress Maximus, but Scorponok warned them not to be naïve for the while the G metal was strong, the Master Sword was massively stronger. He kidnapped Wheelie and ransomed him for the secrets and began to create the Zarak Shield, and despite intervention from the Autobots, managed to successfully construct it. The construction of the Zarak Shield had badly drained their energon supplies, so Scorponok decied to blow up Earth to compensate. He launched a devastating attack on the city and in a duel with Fortress Maximus, managed to defeat his foe, but spared him as he now departed to blow up Earth.
Nevertheless, on the return journey, tensions between him and Sixshot flared when they approached an asteroid belt, and rather than take a detour, decided to recklessly go straight in. When one asteroid knocked him out of the pilot position, Sixshot angrily reprimanded him, and Scorponok furiously stated he had had enough of him and kicked him, driving tensions between the two up. He subsequently abandoned Sixshot, but when the ninja returned, decided to kill both him and Chromedome whom the latter had challenged to a duel. Scorponok presumably succeeded in killing Sixshot, though in reality the ninja had survived.
Returning to Earth, he arranged for the mining and refinement of crysmagmetal from Lemuria, and after a brief confrontation with Fortress in Egypt, departed for Lemuria to confirm the Death Towers and the satellite he had launched were in position. He was then confronted by the living Sixshot, much to the latter's horror. After briefly showing shock, he feigned happiness and revealed his plan to the ninja. Sixshot then announced that he had come to bid farewell. Scorponok angrily accused Sixshot of planning to betray him know that he knew the secret and attempted to kill Sixshot, but only managed to hit one of his holograms. Infuriated, Scorponok vowed to destroy everyone on Earth. In a duel at the North Pole, he fought Fortress Maximus one last time, and once the satellite was in position, fled his Transtector and waited for the destruction of Earth. However though, thanks to Sixshot, the Autobots united and used their combined energy to power up Fortress, enabling him to destroy the satellite, much to Scorponok's horror and shock. Fortress then destroyed his Transtector along with the Zarak Shield, and Scorponok was forced to abandon the Earth.
Scorponok as depicted in The Headmasters, is the malevolent, manipulative, ruthless, power hungry, psychopathic, megalomanical, wrathful, bitter, treachours, mercilees, cruel, arrogant, vain and dictatorial leader of the Devepticon headmasters. He has a fierce lust for power, as shown when he attempted to rebel against Fortress and by his desire to become leader of the Decepticons. Scorponok is extremely intelligent and charismatic, as shown by his ability to incite an uprising against Fortress, and easily managing to convince the Decepticons that he was receiving orders from Galvatron and again when he claimed leadership after Galvatron's death.
Before the creation of his Transtector, Scorponok genuinely relied on technology, and also was highly capable of creating plans that would take out all of his enemies. His skill at manipulation is further shown by goading Fortress into rash confrontatins, showing his skill in psychological warfare. Nevertheless, he is somewhat cowardly, as he does not possess the physical strength of his minions, and has a tenacity to overestimate his foes.
When combined with his Transtector, he possess brutal strength and also easily could turn his oppenents weakness to his advantage. He is also very cruel and sadistic, especially shown during the finale, when he lets the Autobots live to let them watch their beloved Earth die. He is also highly strategic and tactical, preferring strategy and more cautious methods over Glavatron's hot headed approach.
His cruelty is shown when he blows up Cyberton, Mars, and almost managed to destroy Earth, an act that likely killed thousands of humans, if not more and also shown by ordering his minions to kill Tekna simply because the Beastformer knew his weakness. He is also treacherous, as shown when he blew up Cybertron, and presumably killed Galvatron, and betrayed Sixshot despite owing the ninja his leadership, and possibly his life, twice.
Nevertheless, Scorponok also has some errors, the most obvious ones being arrogance and overconfidence. His arrogance has made him make reckless decisions, such as when he ordered the Transtector to fly through an asteroid belt, and his overconfidence was shown during his destruction of Mars and the finale, in the belief he had defeated Fortress and the Autobots. These traits prove to be his downfall as Fortress managed to destroy his satellite, forcing him to flee Earth for good.