Ah, Starswirl. In some ways a very simple character, in others, every bit as complicated as his legacy. In short, he is a cautionary tale of the mistakes Twilight could have made if she’d never matured from her beginning-of-series self and opened herself up to relying on others.
Born to a family that had left the political intrigue of Old Unicornia behind for a more “simple” life as farmers (but weren’t very good at it), when his magic proved to be stronger and more unpredictable than they could handle, his father took him to Everfree Village in search of a mentor he could be pawned off on.
Silver Swirl was more than happy to take him under her metaphorical wing, and even offered him part of her own name when it became clear that his family had essentially washed their hooves of him.
Starswirl was a sharp student, and keen to learn every scrap of magical theory he could get hold of. However, he began to grow dissatisfied with Silver Swirl’s teaching style, particularly her library of disorganized and unfinished spells. What amazing things she could have been capable of if she weren’t so scatterbrained! What amazing things he could do with what she just left lying around!
Secretly, he began taking and modifying them to his own needs, with a great deal of success. Silver Swirl was hurt when she discovered he’d been going behind his back, but praised him for his ingenuity in the spell modifications, and when he struck out on his own as a freelance wizard, she supported him every step of the way.
While he started out with genuinely kind and helpful intentions, the more he interacted with ponies at large, the more disillusioned Starswirl became.
As far as he could see, ponies were expecting “heroes” like him to shoulder all of the problems their continued infighting was causing, while the successive Councils and their guards were largely ineffective at containing the strife.
Even after the future Princesses had been found and brought to Everfree Village to begin their training, he didn’t see any proper future for supposedly-”united” ponykind unless drastic measures were taken.
An idea began to form in his mind. It had taken a threat against all three tribes, the Windigos, to temporarily bring peace. Perhaps it would take another overarching threat to force ponies to come together again.
This plan backfired spectacularly (though we can’t reveal the details just yet as those are spoilers), but it wasn’t until after Twilight’s interference freed the Pillars (and Stygian) that Starswirl learned just how devastating his mistake of hubris was.
Hearing from Sunsparkle’s own ghost that he’d been partially responsible for the death of Majesty, a pony he’d greatly respected even after he’d stopped listening to Silver Swirl, was a big blow to both his pride and his heart.
For the first time, he seriously questioned his judgment in thinking that he and he alone had the answers. That he didn’t need input from anyone else.
For the first time, he realized that he needed to change his methods. Perhaps even… make the effort to actually make some friends?
Guess it’s time for an old pony to learn some new tricks.
Turns out being a crank all your life with a grumpy savior complex kind of gets in the way of that, but bless him for trying because it's really a sight to see