Darth Sidious

"My mentor taught me everything about the Force, even the nature of the dark side."
-Palpatine to Anakin Skywalker

Darth Sidious's apprenticeship has been described as lasting many decades,though there is no specific indication of when it began or when it ended. In that time, Plagueis trained Sidious in accordance with Darth Bane's tradition. During the course of Sidious's training, Darth Plagueis once allowed him access to a number of Sith holocrons, items that, according to the arcane writing inscribed on their pyramidal surfaces, were recorded in the days of Darth Bane. The Jedi mistakenly believed that these holocrons sat in the Archives room in their Temple, but those were actually clever forgeries, a form of Sith disinformation. How the actual and false holocrons came to their respective owners is still not known.

Under Plagueis, Sidious deeply studied Sith history, learning of the ancient Sith Lords as well as the more recent ones, such as Darth Bane. Bane's teachings were of particular note, as they were the basis of the order. Plagueis's teachings were brutal, but they successfully molded Palpatine into one of the most powerful Dark Lords since Bane.
The Murder of Darth Plagueis

Plagueis was obsessed with immortality. He delved into forbidden teachings, and possessed?or sought to possess?knowledge that could sustain those who were dying, or even return them from death.Both the Jedi and the Sith had sought ways to survive death for thousands of years, without success. The most powerful of the ancient Sith Lords, particularly Darth Sion and Darth Andeddu, supposedly knew such secrets, but they had been lost or misplaced. Plagueis then began taking his research to its greatest extreme, to create new life from nothing. Eventually Plagueis told Sidious of an experiment to influence the midi-chlorians to draw life directly from the Force itself. The child that resulted, Plagueis insisted, would potentially possess astounding powers.

Sidious at once suspected that Plagueis's real intention was to "create" a new apprentice to replace him. His position threatened, Sidious decided that he had learned all he could from Plagueis, and he already had his own secret apprentice in the form of Darth Maul. Soon after, Sidious killed Plagueis in his sleep and took the title of Sith Master for himself. To make certain the same thing would never happen to him, he kept a close eye on his own apprentices, and told them only the barest minimum of information about Plagueis.For much of his life, he would be on his guard, vowing to himself never to make the mistake of sleeping as Plagueis had.

Though Plagueis had died, there is evidence to suggest that his experiment came to fruition nonetheless: on the distant desert world of Tatooine, a thirty-year-old slave woman, Shmi Skywalker, gave birth to a son, named Anakin Skywalker (42 BBY). Though much remains unknown about Skywalker's childhood, it is known that his mother had no knowledge of her son's biological father, and when Skywalker eventually became known to the rest of the galaxy, it was discovered that he had more Force potential than any Force-user in history: his midi-chlorian count passed 20,000 per cell, far beyond the most powerful Sith or Jedi(by contrast, the average count for a standard, non-Force-sensitive human was less than 2,500 per cell). Sidious kept a close watch on Skywalker as he grew, anticipating that he could be a far more powerful apprentice than Darth Maul