Born during the height of the Jedi Purge, Galen Marek, aka Starkiller, was born to Jedi Knight Kento Marek and freedom fighter Mallie also a member of the Jedi Order. The two married in secret during the Clone Wars and escaped order 66. Galen was born on the run, and grew up knowing only fear of the empire. He had an extremely strong connection to the force which made it difficult for the two running Jedi to hide from Vader's senses. Together the three settled on Kashyyyk in hopes of the vast jungle masking their presence. Vader however; personally led the mission to find them on Kashyyyk killing countless wookies and laying waste to the planets forests. Upon locating and killing Kento Marek, young Galen used the force to pull Vader's saber out of his hands, leading Vader to kidnap the child and begin raising him in secret.
Taken on board Vader's unfinished ship The Executor, Galen was hidden away from prying eyes and trained relentlessly in the ways of combat and how to master his force abilities. The brutal lessons Vader taught young Galen bordered on torture, and nearly drove him insane with hatred. Taught to hide all memories of his past, Galen nearly forgot who he was and how he had come into Vader's control. He was given a sparring partner named PROXY, a holodroid capable of storing the personalities and abilities of various Jedi. While Vaders methods were brutal, much of the abuse was also self inflicted, with Starkiller pushing his will to the limit by forcing PROXY to seal him away with no food or water until he had accomplished his goal. Starkiller was however unable to experience visions of the future due to his clouded outlook, and thus was often caught off guard by new tactics used in his training.
Starkiller became Vader's personal assassin taking small missions to assassinate Imperial targets and enjoying it, believing that he was doing his Imperialistic duty. Though Starkiller was a skilled pilot, Vader insisted that he meditate and focus during the flight to gain a deeper knowledge of the target. During a mission to Duro, Starkiller encountered an much heavier resistance than he had been led to believe and developed a strong dislike for AT-ST's. During a sparring session with Vader, Vader commanded he kneel. Thinking this to be his death, Starkiller obliged and was surprised when Vader knighted him declaring that he was now truly an apprentice.
During his training, Starkiller was sent to the Jedi temple 3 times, for a trial of skill, a trial of Insight and a trial of Spirit. Upon the first of these, he encountered a hologram warrior of Darth Desolous barely defeated it. Upon the second trial, Starkiller encountered imperial Sentinels blocking his path, which he defeated and ventured in again, this time facing a holographic warrior taking the personality of Darth Phobos. After a long battle in which Starkiller was forced to fight with a more passive attitude, he defeated the hologram. Upon the third and final trial, Starkiller witnessed a vision of the battle of Vader against his Father Kento, not knowing it was his father, leaped to Vader's aid. He defeated the strange Jedi and only moments after discovered it had been his father. He began searching for knowledge of his father but only encountered a dark entity that matched him in every way. After a very long fight, Starkiller defeated his dark reflection and left the Jedi Temple for good.
He was then deemed powerful enough to embark upon Jedi hunting missions, the first of which was against Jedi Master Rahm Kota, whom Starkiller blinded and threw from a falling and space station. The next assignment pitted him against rouge Jedi Kasdan Paratus who had gone mad on Raxus Prime. He was defeated by Starkiller stabbing him in the chest. Finally Starkiller encountered Jedi High Council Member Shaak Ti. Following a viscous battle, Starkiller mortally wounded her, before she threw herself into the great Sarlaac pit. Starkiller was now ready to take on the Emperor, but was betrayed by Vader and Stabber, had his bones broken, and was thrown into the vacuum of Space.
Vader recoverd Starkiller's nearly dead body and revived him, claiming that he still had need of him. Vader commanded Starkiller to begin forming an army of rebellions to distract the Emperor so that together they could still overthrow him. Acting upon this, Starkiller began a brutal assault on Imperial targets, killing any in his path, and finding allies such as the wounded and now drunkard Rham Kota, Bail Organa, And young Leia Organa. Rham Kota began acting as a master to Starkiller and helped him relax his mind allowing him to finally be able to sense the future.
After being betrayed by Vader a second time when he stormed the rebels meeting on Corellia, capturing the leaders, and Master Kota, Starkiller became enraged and led an all out assault on the Death Star alone. He fought his way to the Emperors chambers, encountering Vader along the way. Starkiller destroyed Vader's helmet and threw him at the Emperors feet. Upon seeing this Sidious offered Starkiller a place as his apprentice if he killed Vader. Kota intervened and attacked the Emperor, and Starkiller went to his aid battling against the Emperor, but ultimately sacrificing himself so that his new allies could escape. He became a very powerful symbol to the new alliance and his memory lived on with the rebellion, who turned the Marek Crest into the rebel insignia.