Acastus Kolya was a Commander in the Genii military and an enemy of the Atlantis expedition, particularly the First Atlantis Reconnaissance Team with Kolya being a personal enemy of both Dr. Meredith Rodney McKay and Major/Lieutenant Colonel John Sheppard up until his death at the hands of Sheppard in 2006.
During the storm season on Lantea, Chief Cowen ordered Kolya and his strike force to raid Atlantis for their supplies of C-4. Kolya advised against it, citing that his team was not ready for such a mission, but Cowen insisted that this was their only chance. He carried out Cowen's orders and took control of Atlantis, killing two soldiers over the objections of Sora Tyrus. Upon learning of the plan to save the city, he decided to enact a more ambitious plan of taking the entire city. Sora protested that they did not have the resources to conduct such a mission, but he insisted. This proved to be his downfall, as Major John Sheppard was able to thwart his efforts, systematically killing Kolya's strike force and taking out an entire company of reinforcements by activating the Stargate shield. When it appeared as if the plan to save Atlantis would fail, Kolya decided to withdraw, planning to take Dr. Elizabeth Weir and Dr. Rodney McKay with them. As Kolya and his men retreat through the Stargate, Sheppard and Lt. Aiden Ford mount a rescue, killing several more members of the strike force, excluding Ladon Radim and a few others who make it through unharmed and rescuing McKay. Kolya attempts to make it through the Stargate with Weir as a human shield, but Sheppard is able to hit him in the shoulder with a precision shot from his FN P90 Personal Defense Weapon. The force of the shot causes Kolya to let go of Weir and fall through the Stargate alone. (SGA: "The Storm", "The Eye")
The failure of the Atlantis raid forced Kolya from Cowen's inner circle and shattered his standing amongst the Genii. Upon hearing that Major John Sheppard's team was close to recovering a Zero Point Module, but unable to get authorization to stop them, he organized a small team to steal the ZPM from them, both because he thought the Genii had a better use for it and to deny them the ability to use it. Though he was able to trap them in an underground chamber, he failed to completely disarm them and Ford still carried stun grenades. After retrieving the ZPM, Ford set off the grenades and as Teyla and Ford engaged his men, Sheppard engaged Kolya. Sheppard quickly overpowered Kolya and recovered his P90 from him, leaving Kolya on the floor stunned. Sheppard decided to let him live, despite Kolya recommending that killing him would be better. Sheppard told Kolya that he wanted points for sparing him, but promised Kolya that if he crossed with him and his team again, he would kill him. (SGA: "The Brotherhood", "Common Ground")
With Cowen's ambitions growing and seeing his regime as more and more corrupt, Kolya began planning a coup took into his confidence Ladon Radim, Cowen's Chief Scientist and a former member of Kolya's strike force. However, Ladon didn't feel that either man was fit to rule and instead betrayed Kolya to Cowen, forcing Kolya underground. While planning his own coup against Cowen, Ladon tells the Atlantis expedition that Kolya was the one man capable of standing up to Cowen and has disappeared, possibly murdered by Cowen. (SGA: "Coup D'etat", "Common Ground")
Months after Ladon successfully overthrew Cowen, Kolya sets a trap for the First Atlantis Reconnaissance Team and captures Lt. Colonel John Sheppard. Kolya explains Ladon's betrayal of him to Sheppard and contacts Atlantis, demanding that they turn over Ladon in exchange for Sheppard. When Weir refuses, Kolya has a captive Wraith brought in to feed on Sheppard briefly. Kolya then gives Weir three hours to decide whether or not to turn Ladon over. When the time is up, Weir refuses again and again Kolya has Sheppard fed upon. Kolya tries one final time three hours later and when Weir refuses, tells the Wraith to "take your fill." After feeding on Sheppard for a time, the Wraith stops and asks if Kolya would like him to finish. Kolya sends the two back to their cells and gives Weir two hours. However, Sheppard and the Wraith, who he later names Todd, form an alliance and escape Kolya's prison complex together. Kolya sends his men to both guard the Stargate and search for the two. After a Puddle Jumper arrives with a rescue team from Atlantis, Kolya realizes he's beaten and decides to flee through the Stargate with his remaining men rather than face Sheppard's team. Before he departs, Kolya is contacted by Sheppard who has had his life restored over a Genii communicator. Sheppard states that he figured Kolya would run and promises that the next time they meet, Sheppard will kill him on sight. Kolya listens to Sheppard's warning, but doesn't respond before he escapes through the Stargate. (SGA: "Common Ground")
After being humiliated by Lucius Lavin, Haemon, a former Genii soldier, alerts Kolya to the fact that Sheppard and his team are on M65-PL8. Kolya leads his men to the village on the planet in order to kill Sheppard and capture the rest of the team to use in trade for weapons with Atlantis so he can overthrow Ladon. When Lucius tries to intervene, Kolya becomes intrigued by his Ancient personal shield emitter and tortures Lucius by holding his head under water until he gives up the team's location. After failing to find them, Kolya threatens to bury Lucius alive and leaves him strapped to a bomb as bait. Though he fails to capture Sheppard, Kolya manages to capture the rest of his team and Doctor Carson Beckett.
Kolya explains his intentions to the team and uses a Tau'ri radio to inform Sheppard that his men are guarding the Stargate and he will kill McKay if Sheppard fails to surrender. Sheppard agrees to surrender, but when he fails to return quickly enough, Kolya prepares to execute McKay and is amused by Teyla, Ronon and Beckett offering themselves up first. Sheppard finally arrives and after the two acknowledge they should've killed the other when they first met, Kolya orders his men to fire. However, Sheppard is protected by Lucius' shield and Kolya's men fail to harm him. As Sheppard taunts Kolya, his shield runs out of power and Kolya orders his men to reload. Before they can, Lucius arrives with the townspeople who surround Kolya's men who are forced to surrender. When offered the chance to surrender himself, Kolya simply chuckles and he and Sheppard enter an impromptu duel. Though both are able to draw their guns, Sheppard is the faster shot and he shoots Kolya in the heart, finally killing him. Beckett is able to confirm his death afterwards. (SGA: "Irresponsible", "Remnants")
Seeing Sheppard as a possible threat to its mission, the Sekkari seed carrier's AI sought to distract Sheppard and took on the form of Kolya for this purpose. As Kolya, the AI claimed "he" had survived using Ancient technology. The AI maintains the illusion that Kolya and his men are chasing and torturing Sheppard until Sheppard's life is genuinely in danger and stops. Afterwards, the Sekkari AI uses Kolya's form to communicate with Sheppard directly and explain its purpose. The AI tells Sheppard that the illusion with Kolya was based off of Sheppard's own mind and thoughts and indicates that in a way, it was Sheppard torturing himself. (SGA: "Remnants")
Kolya was dedicated to the betterment and survival of the Genii, to the point that he was willing to do anything to achieve it. Kolya had no compunctions against torture and murder, even being willing to kill unnecessarily such as murdering the two Atlantis guards when his strike force could've easily overpowered them. However, Kolya was not completely cold-hearted and was visibly distressed by the deaths of Pranos and his friend Athor's son Idos as well as over 60 Genii soldiers. He was also distressed by McKay's implication that he was responsible for Pranos' death with his impatience, particularly as Pranos was his friend. While willing to use a Wraith feeding on Sheppard as a form of torture, Kolya admitted that no one deserved that, not even Sheppard though he was willing to do it. Kolya was also greedy to the point of it being a weakness. His greed to take Atlantis whole rather than just raiding it for what the Genii needed and then to hold it even after the deaths of his men, led to his ultimate downfall in the Genii invasion of Atlantis. If Kolya hadn't insisted on attempting to maintain control over Atlantis, despite heavy casualties, he would've been able to at least accomplish the Genii's original goal. Similarly, his use of Todd torturing Sheppard to get Elizabeth Weir to hand over Ladon Radim was greedy and overly ambitious. Kolya himself later recognized this and set his sights lower when he next encountered the Atlantis expedition, aiming for a more reasonable demand. Kolya has also shown an unwillingness to give up even when beaten as best demonstrated by his refusal to surrender moments before his death despite being heavily outnumbered and alone.
Due to the events of the Genii invasion of Atlantis, Kolya held a mutual hatred for John Sheppard, particularly given how many of his men Sheppard had killed during the invasion and how many defeats Sheppard had dealt him. Sheppard noted at one point that Kolya would kill Weir and McKay simply to hurt Sheppard. Kolya was also more than willing to use Todd to drain Sheppard's life a little at a time as a form of torture. Despite this, Kolya is shown to have a measure of respect for Sheppard and his abilities, calling Sheppard "an exceptional soldier" who requires exceptional measures to bring down. On another occasion, Kolya admits that no other enemy has ever given him as much trouble as Sheppard and he should've killed Sheppard when they first met as it would've saved him a lot of trouble.
After Kolya's capture of Sheppard, Ladon indicates that there was more to Kolya than the Atlantis expedition knew. Ladon stated that of course they would only see Kolya as the man who invaded Atlantis and killed several of their people, but indicates that there was more to him than that that they didn't see. It was indicated that his later actions were driven by Ladon's betrayal of Kolya and his being forced from his people. Ladon notes that Kolya also found Cowen's regime to be corrupt and was the one man who could stand up to him. However, while Kolya was willing to overthrow Cowen, he also felt that he was the only rightful leader of the Genii.
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