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.

How did they clone Starkiller?

Six months after the death the original Starkiller, Darth Vader took his body to Kamino and cloned him, hoping for a more powerful and obedient version of his deceased apprentice. After a series of deranged and deformed clones resulted in numerous failures, Vader finally created a stable clone of Starkiller.

Is Starkiller a clone of Anakin?

The dark clone of Anakin Skywalker, who later take on both of the names of his genetic template, first Anakin Skywalker, and later on Darth Vader, was a human male cloned by Starkiller from the genetic material of his former master, Darth Vader.