Following Galen's death on the Death Star and the revelation that the Emperor wouldn't hesitate to replace him, Vader took Galen's corpse to Kamino where he began a top secret project to create the perfect clone of his dead apprentice. Due to the inherent difficulties of cloning a Force-user at an accelerated rate, the Kaminoan scientists were met with repeated failure as the clones were either physically or mentally unstable, resulting from residual memories from Galen's life. Many of the clones went insane as a result of this or were deemed failures by Vader for being unable to strike down holographic versions of Juno due to them inheriting Galen's feelings for her.
Eventually they succeeded in creating a stable clone who would later come to be known by Galen's former codename 'Starkiller' . Despite being genetically identical to Galen and being immensely powerful, Starkiller was deemed to be a failure by Vader after he refused to strike down Juno, unable to overcome Galen's affection for her.
Starkiller was created to replace the original so as to continue the Star Wars: Force Unleashed franchise. He was created by Haden Blackman.
Major Story Arcs
Force Unleashed II
Vader informed Starkiller that the accelerated cloning process was still imperfect, which caused the clone to experience a memory of Vader literally stabbing Galen in the back aboard the Executor. Realizing that Vader was going to kill him, Starkiller turned on Vader and escaped Kamino in search of Juno, who had become an obsession to him.
Starkiller made his way to the Imperial garrison on Cato Neimoidia where he rescued Galen's former teacher and ally Kota from the gladiatorial arena, single handedly defeating a colossal Gorog beast that the Imperial overseer had unleashed on them. After escaping the planet aboard the Rogue Shadow, Kota, unaware that Starkiller was a clone of Galen, informed Starkiller that Juno was with the rest of the Rebel Alliance, which was in danger of being defeated and requested that he lead the Alliance against the Empire. However Starkiller revealed his true nature as an imperfect clone created to replace Galen to which Kota replied that it was impossible to clone Jedi, creating much confusion for the clone, who at this point only wanted to find Juno.
An accidental slip by Kota led Starkiller to Dagobah where he encountered Yoda and unaware of the Jedi master's true identity, Starkiller went into a cave where he experienced a powerful series of visions which culminated in his learning the location of Juno and the rest of the Rebel Alliance. However he also witnessed a vision of the Alliance fleet being attacked and Juno captured and Starkiller 2 immediately traveled to rendezvous with the fleet, docking with Juno's new frigate the Salvation. While nervously awaiting his first meeting with Juno and fearing the attack in his vision coming to pass, Starkiller gave Kota valuable strategic information on the Imperial forces stationed on Kamino, which would be a tremendous victory for the Alliance.
Shortly after they docked however, the fleet was attacked by an Imperial strike force and the Salvation was boarded with enemy troops, as well as a series of droids designed to tear the ship apart from the inside. Making their way to the bridge, Kota and Starkiller found the bridge crew had been slain and Juno abducted by a bounty hunter, who was later revealed to be Boba Fett, who had kidnapped her on Vader's orders, knowing that Starkiller would follow them back to him. Starkiller also found PROXY, who had been retrieved and re-activated by Juno and both expressed surprise that the other was alive before PROXY directed the clone to where Fett was taking Juno.
However Starkiller was unable to rescue Juno as his path was blocked by a powerful droid which kept him busy long enough for Fett to escape the Salvation with Juno, taking her to Vader who was waiting for them on Kamino. After clearing the Salvation of enemy forces, Starkiller ordered Kota to take the fleet to Kamino in pursuit, intending to launch an immediate attack on the Imperial facilities there but Starkiller's only real interest was rescuing Juno. When the Alliance fleet arrived at Kamino, they came under attack from the Imperial vessels in orbit around the planet and Starkiller ordered all remaining personnel to abandon the Salvation before setting a collision course with the cloning facility on the surface, using the already heavily damaged Salvation to break through the Imperial defence shield and allow Alliance troops to begin a ground assault.
As he battled through the Imperial forces in the facility, Starkiller willingly abandoned Kota and the rest of the Alliance troops in favour of getting to Juno and as he made his way into the restricted cloning area, he was assaulted by visions of Galen Marek's life to the point that he was barely able to concentrate. However he continued to press on and found himself in a massive laboratory that was filled with countless cloning pods that were incubating Galen Marek clones. Vader was there waiting for him and the two engaged in a vicious duel that wrecked most of the lab and forced to retreat, Vader set a number of failed clones on Starkiller, who was forced to kill his genetic 'twins' in order to pursue Vader.
Catching up to Vader at the top of the cloning tower, Starkiller saw Juno in restraints by Vader's side and she expressed mixed shock and happiness at seeing him alive, even though she had been made aware that he was probably a clone of Galen. Vader began to choke her with telekinesis and, desperate to keep Juno alive, Starkiller willingly submitted to Vader and dropped his lightsabers, agreeing to Vader's orders to hunt down and eliminate the Alliance leaders as well as return to him as Vader's apprentice. However Juno discreetly grabbed one of Starkiller's lightsabers and tried to kill Vader from behind but Vader easily defended himself against her before throwing her out the window, seemingly killing her as she landed on a nearby landing pad below.
Enraged by the apparent death of Juno, Starkiller attacked Vader in a murderous frenzy, pummeling the Sith lord relentlessly and the fight moved out on to the landing pad where Juno's body lay. Starkiller redirected a bolt of lightning at Vader, severely crippling him and was about to kill Vader when Kota arrived, arguing with the clone to keep Vader alive for interrogation and eventual execution to show that the people no longer needed to fear the Empire. After much struggle, Starkiller eventually lowered his lightsaber and allowed Kota and his men to take Vader into custody, before heading to Juno and lamenting that if he had just stayed on Kamino in the first place, she would still be alive.
Cradling her body, Starkiller was shocked when Juno was revealed to have miraculously survived her fall and kissed him. Together with Juno, Kota and PROXY, Starkiller left Kamino aboard the Rogue Shadow which was going to transport the captured Vader to a rebel base on Dantooine but as they leapt into hyperspace, they were unaware that Boba Fett was following them, apparently with the intention of freeing Vader.
Dark Side Ending
After Starkiller 2 has defeated Darth Vader on Kamino, he is implored by Kota to spare the Sith lord but chooses to execute Vader in revenge for Juno. However before he can kill Vader, he is stabbed from behind by an invisible figure wielding a lightsaber. The attacker turns visible and quickly kills Kota and his Alliance troops and is revealed to be another clone of Galen Marek, although this one has given himself completely to the dark side and become the true Sith apprentice that Vader had intended to create. Vader coldly informs the dying Starkiller 2 that he had lied when he said the cloning process hadn't been perfected and Starkiller 2 takes one last look at the dead Juno Eclipse before dying himself.
The Dark Apprentice then kneels before Vader, who orders him to take the Rogue Shadow and hunt down the Rebel Alliance leaders and execute them, before taking on their ultimate goal of defeating the Emperor. The Dark Apprentice calmly accepts this mission and pauses only to look coldly at Juno's body, remembering but unaffected by Galen Marek's memories of her before proceeding on his mission, leaving Kamino on the Rogue Shadow before jumping to hyperspace.