Sensing the potential within Marek, Darth Vader killed the child's father and took him to be trained in the ways of the dark side of the Force.
Legends. Galen Marek, codenamed Starkiller, was the son of a Jedi fugitive killed by Vader during the Great Jedi Purge. After his father's death, he was trained by Vader since childhood to become the Sith Lord's secret apprentice.
Darth Vader cared for Galen Marek aka Starkiller as much as any Sith Master cares for his Apprentice.
Galen Marek was taken from Kashyyyk in 18 BBY by Darth Vader, who trained him to become his apprentice, giving him the codename 'Starkiller', with the intention of overthrowing Emperor Palpatine. After 15 years of training, Vader sent him to hunt down Jedi such as Masters Rahm Kota and Shaak Ti.
In Star Wars Legends and Canon, Galen Marek (Starkiller) is the only Jedi (other than Obi-Wan Kenobi) to put a beat down on Darth Vader/Anakin Skywalker.
1 Darth Sidious
As well as being a gifted bladesman Sidious' connection to the Dark Side is extremely powerful, granting Sidious the ability to conduct force lightning.
Darth Vader Kills Starkiller (Star Wars The Force Unleashed) - YouTube.
Lord Starkiller, born Galen Marek, was a 20 year old Human male, and Dark Lord of the Sith. He was born in 18 BBY to two Jedi on Kashyyyk. He is the apprentice to Darth Sidious, and master to Darth Karidius, formerly Luke Skywalker.
Starkiller, also known as Galen Marek, the main character of Star Wars: The Force Unleashed.
On Kashyyyk, Starkiller experiences a vision in the Force, in which he finds his body altered into the Sith Warrior's armored appearance. As he duels with a Jedi Knight version of himself, Starkiller all but completely surrenders himself to the dark side and is thrilled by the power he gains through it.
Even after his brutal scorching in the fires of Mustafar, sand remained the only natural phenomenon that Vader feared. To him, sand was a reminder that he'd failed to save his mother or Padme from death.
Starkiller's death at the end of the first game, sacrificing his life against the Emperor to save the leaders of the Rebel Alliance, with even Vader visibly and audibly saddened in the aftermath, who despite everything else he was and had done, had been the closest thing to a father that Starkiller had.
The renegade clone of Anakin Skywalker was a human male cloned by Starkiller from the genetic material of his former master, Darth Vader. Following Vader's death, Starkiller embarked on a quest to create a perfect, obedient duplicate of the man to take as an apprentice.
Starkiller's overpowered nature may be due to a range of influences, most notably his training under Darth Vader which helped to grow feelings of hatred and anger within him to build his naturally-significant strength.
Luke Skywalker was originally going to be named “Luke Starkiller” in the early drafts of the 1977 film. However, according to an article in Yahoo! , Lucas would eventually change the name to “Skywalker” due to what the creator would refer to as “unpleasant connotations.”
Starkiller replaced his lightsabers' synthetic crystals, changing the color of the blades to blue. While traveling throughout the galaxy in an attempt to locate Eclipse, Starkiller had numerous occasions to use his dual-lightsabers in combat.
As a Grey Jedi independent of the Jedi Order, Galen followed the force how he saw fit, relieving himself from being blinded by either of the main ideologies of the Jedi or Sith Orders. He believed the Force is a great power that should be explored openly, dismissing any restrictions placed over the Light or Dark.
Though trained in the ways of the Sith, the Rule of Two dictated that there could only be two Sith at a time, and therefore Starkiller could not consider himself a true Sith while his master was still apprenticed to Darth Sidious.
However, Starkiller was a master of the Dark Side, and was not about to be overpowered by this newly fallen Jedi.
Subject 1138, also known as "Starkiller," was a clone of Galen Marek, a Force-sensitive Human male trained by the Sith Lord Darth Vader as his secret apprentice.
Master Yoda has risen above all others to claim the top spot as the most powerful Jedi of all time and the true chosen one according to IGN's audience. He won pretty handily as well, as he was victorious in 89,756 of his 95,243 battles and had a win percentage of 94.2%.
Despite spending the majority of his life under the tutelage of Darth Vader, Starkiller never became a true Sith Lord. Rather, he is considered to be a Dark Jedi, one of numerous Dark Side acolytes trained by the Empire.
Taking on his birth name, Galen Marek abandoned the name Vader gave him. He took control of his own destiny and went to free the Rebels, now considering himself a Jedi and a Rebel. When faced with the choice, he decided to give his own life so the Rebellion could survive rather than attack Vader and the Emperor.
starkiller is very strong. But Luke is simply stronger in every possible way. Starkiller defeated Luke in Hoth, but it was Luke before he started his training, and he showed strong enough control in the Force to fight Starkiller.
In short, while Galen Marek was a powerful Force-user, he was not truly the strongest Sith in any Star Wars canon.