Galen Marek, codenamed Starkiller, was a male human Sith apprentice of the Sith Lord, Darth Vader. A powerful Force-user who lived during the era of the Galactic Empire, Marek originated from the Wookieehome planet of Kashyyyk as the sole offspring of two Jedi Knights—Mallie and Kento Marek—who deserted the Jedi Order during the Clone Wars. Following the death of his mother, the young Marek's father was killed in battle by Darth Vader. Though only a child, Marek possessed an exceptionally strong connection to the Force that the Dark Lord of the Sith sought to exploit.

It is unknown what sort of child Galen Marek was, but what is known is that when he stood against Darth Vader, wielding the Sith Lord's own lightsaber against him, he did so out of a desire for vengeance after his father's murder. This desire marked Marek's first step towards the dark side, and Vader recognized this in him. Despite this desire for vengeance, he was not yet completely fallen, still being traumatized by Vader's massacre of the Stormtroopers immediately afterwards. All of these traumatic events would cause Marek to repress all of his childhood memories, and forget his own name, though his initial step towards the dark side remained a permanent part of his personality for much of his life.

Though he was brutally and continually punished by his master, Starkiller submitted willingly to the teaching method of the Dark Lord, essentially because he knew nothing else, and this instilled in him the belief that whatever did not kill him would make him stronger, more adept at wielding the dark side. Such was Starkiller's state of mind towards the end of his training, a part of him almost wished for death. His subjugation to Vader even displayed itself in his voice and manner, as he affected a formalized and faintly aristocratic accent whenever he was in Vader's presence, in stark contrast to his usual behavior. In addition, due to his life-long isolation from all but a few individuals, Starkiller was reclusive, and emotionally remote to all but PROXY.

When hunting down and dispatching his targets, Starkiller was always satisfied that he had helped defend the Galactic Empire and fulfill his master's will. While powerful and confident, Starkiller demonstrated many different sides to his personality. He was wary of his purpose in life and what he was meant to do; he began with a sure focus on the Sith destiny trained into him by Vader. However, his exposure to both the Jedi, the light side of the Force, and also to the reality of Sith life caused his focus to waver. Ultimately, his innate sense of loyalty proved incompatible with Sith philosophy, and he gradually made his choices in life accordingly.

Galen Marek should sound like his voice actor, Sam Witwer.