I was thinking earlier today about starting another off-topic thread so more people had more opportunity to get their first 10 approved posts in. I was originally planning to create a "Which movie and EU characters inspire you the most?" question thread, but in the process of thinking how I would personally respond I started thinking.
For EU, my answer would have to be Darth Bane. His story takes him from being what was essentially a slave on a remote mining planet to being an accomplished soldier who would eventually become one of the most accomplished Sith Lords in the now Legends canon. His largest accomplishment was called the Rule of Two.
After living through a period where the Sith matched, if not exceeded, the Jedi Order in numbers, Bane came to the conclusion that their numbers were weakening the Sith as a whole. Since the environment promoted advancement via betrayal, he noticed that the objectively stronger Masters were being taken down by groups of weaker apprentices, who would then squabble for the master's mantle. To prevent this, Bane determined that the Sith would only succeed if it encompassed only a single master and a single apprentice: one to have the power, and one to crave it. The master would teach the apprentice until the point came where the apprentice would be powerful enough to challenge and defeat the master, ensuring that the next generation became stronger. This thinking led Bane to destroy the Sith as they were and take on an apprentice named Zannah, leading a new Sith Order that thrived on subtlety. Eventually his philosophy culminated in Palpatine, a Sith with the power to overthrow nearly the entire Jedi order.
Luke's journey seems to mirror Bane's, in a way. Both begin in the lower-caste on remote planets (Dessel vs Tatooine), only to escape by joining an army (the Brotherhood of Darkness vs the Rebel Alliance) where they eventually gain a leadership role because of their strength in the force. While Bane tricked the Brotherhood into destroying themselves so he could become the remaining Sith Lord, the Jedi order of Luke's time was dead or dying; with Yoda's death, Luke became the Master.
At his point, the two diverge (due to the unique circumstances of their times, Bane's advantage of immersing himself in Sith culture and history in the Brotherhood's library, and the general attitude of the Jedi vs the Sith). Bane implemented his Rule of Two, while Luke believed the best path was to begin training a new generation of Jedi. The differences in results becomes apparent. Bane's lineage nearly accomplishes his goal (though fails due to Palpatine's arrogance, ironically) of eliminating the Jedi as a threat, while Luke is thrown down by his own apprentices who don the mantle of the Knights of Ren. In fact, his own nephew becomes the apprentice of Supreme Leader Snoke. The Knights lacked the focus on the individual that the Old Republic Jedi had, where each Master had a single student, and thus became a threat that the Jedi had never had to handle before.
I believe that Luke did not run away to the weird monastery out of shame or fear at what happened with Kylo Ren. Rather, I believe he decided that, in order to defuse this new threat, he would need to take on the mantle of subtlety. He would train a new apprentice in secret, waiting for the moment the Force brought the most promising student forward. In teaching her alone he could ensure that she receives the full of his knowledge and wisdom, hopefully creating a Jedi who could wind up surpassing him. A weird light-side version of the Rule of Two- not out of worry that the apprentice would 'cheat' and weaken the order as a whole, but out of worry that they might not be strong enough to resist the pull of the dark side.
We see something new in Kylo Ren as well. A struggle with temptation against the lure of the light side. Again, this seems to be something unheard of in the Sith lineage until Vader ended Bane's legacy with the destruction of the Emperor.So what we end up with is a Jedi Order that is taking up traditional Sith tactics and a Dark Jedi organization that seems to be developing classic Jedi struggles. A weird reversal of things.
If a happy ending is to be reached in the series, we need to assume that Rey will succeed in surpassing Luke and defeating/turning Kylo and Snoke. I believe the change in Dark vs Light side mechanics we see in the new movies will be the cause of Rey's victory. History tends to repeat itself: the Rule of Two is a tried and true tactic, and the struggle with morality led to both Vader's fall to the dark and his fall to the light. I'd wager that, by the end, we'll see Rey with Kylo as her apprentice and both Luke and Snoke out of the picture.
Let me know if there are any faults here, I typed this up during lunch and probably didn't think it through completely.