The animated series Star Wars: Rebels was better than the theatrical features at building the mythology of the mystical Force. Unlike the films, Rebels was able to take the time to explore the Force beyond the nebulous definition of Light and Dark sides.
Airing from 2014 to 2018, Rebels really dug deep into what the Force really was, and how it affected the universe. And there's no part of the Force more interesting than Bendu.
The Center of the Force
While the main canon tends to be a lot more emphatic about the Light Side and the Dark Side of the Force, Star Wars has a long relationship with exploring the intermingling of the two both in their Legends continuity and in shows like Star Wars: The Clone Wars and Rebels. While the most common narrative presented to audiences is that there is a good and a bad to everything, there is in fact a space of neutrality in the direct center of The Force. It's called Bendu.
Bendu is a giant creature who inhabits the remote planet of Atollon. He is so large that he almost resembles one of the many mesas dotting the desert landscape, and his sensitivity to the Force and years of ancient wisdom make him one of the most powerful Force masters in the Galaxy. Unlike other masters like Yoda or Palpatine, however, Bendu does not belong to either side.
Training Kanan
Bendu first came into contact with the cast of Rebels when the blind Jedi Knight, Kanan Jarrus, despaired at his recent handicap. In one of his darkest moments, Kanan heard Bendu calling out to him through the Force and ventured away from the Rebel's Chopper Base to meet the creature. It was under Bendu's guidance that Kanan learned to "see" through the Force, and the apprenticeship fostered a greater understanding of the world around him and how Kanan could best train Ezra Bridger.
Bendu further provided guidance to Ezra directly and even oversaw Sabine Wren's training with the Dark Saber when the young Mandalorian struggled to learn how to use the blade. The creature was seemingly an unending well of wisdom and guidance to the Rebels at a time when they most needed it but eventually, his goodwill would only go so far. After all, the very essence of neutrality that Bendu represents can't unfairly favor one side over the other.
Bendu's Rage
Ultimately Bendu's swan song in Rebels came when the evil Grand Admiral Thrawn discovered the Rebel base on Atollon. Severely outgunned and outnumbered, Kanan realized that the only chance of evening the score was to appeal to the most powerful force of neutrality in the world. When Bendu at first refused to intervene, Kanan accused him of cowardice and unleashed Bendu's rage. Bendu created a powerful storm that demolished the Rebel and Imperial forces alike. While the Imperial forces tried to attack Bendu, the Center of the Force left as suddenly as he'd appeared.
In the end, Bendu helped unleash the same prophecy of Thrawn's death that he foresaw, and the actions of his apprentices Ezra and Kanan ultimately lead to fulfilling the grander prophecy that balance would one day be restored to the Force. Outside of that and some scant details provided by Rebels creators, there has been very little mention of Bendu. It's doubtless that he's out there, however, and with the balance of the Force so frequently threatened it's only a matter of time before he appears again.