All of the most fantastic elements of Avatar: The Last Airbender's world involved spirituality, with life energy known as chi flowing through the chakras of all living things, and the Spirit World constituting a non-material plane filled with wonders beyond human comprehension. Interestingly enough, mastery of chi energy and chakras was not limited to Benders, and anyone spiritually attuned enough could learn the universe's secrets. But out of every spiritually attuned character in the series, a few stand above the rest.
5. Ty Lee
Although very little is known about Ty Lee's relationship with the Spirit World and the arts of meditation, she was nevertheless a formidable force due to her ability to perceive and manipulate the lines of energy within the body. Often commenting on the "aura" of those around her, Ty Lee had an apparent ability to read others based on sight alone, though it often came across rather hippie-ish. However, the young acrobat was most known for using the art of chi blocking, allowing her to strike precise pressure points and paralyze opponents' limbs and bending.
The ability to block chi made Ty Lee a top-notch Non-Bender, competing with her element wielding counterparts by taking their elements out of the equation. Combined with her acrobatic talents, Ty Lee was a deadly force on the battlefield, so it's easy to forget that her ability to perceive aura and apparent development of the chi-blocking art would spark a revolution years later and paint her as a true master of the spiritual arts. Outside of the acupuncturist Guo, seen in Korra, almost nobody else had the ability to perceive auras or chi in the way Ty Lee could.
4. Unalaq
Of course, some talents are exclusive to Benders, and Unalaq debuted a previously unseen ability in the second season of The Legend of Korra. Harnessing his waterbending into spirals around malicious spirits, Unalaq could manipulate their energy to dissipate them, rendering them inert. What's more, he even threatened to do the same to the spirit of Jinora and to the Avatar herself, showing that his spiritual arts could have lethal applications.
However misguided he may have turned out to be, there's no doubt that Unalaq dedicated his life to understanding the Spirit World and unlocking its secrets. Though his skills in meditation were virtually unseen, the sheer impressiveness of being able to spirit-bend an entire small army that was threatening the Northern Water Tribe proves that he possibly had the rawest power of any spiritual master. Though he promised to teach Korra his secrets, she learned very little from him before his evil nature came to light. By then, Unalaq was ready to show off a whole other talent, fusing with the spirit Vaatu to become the first Dark Avatar in history. Yikes.
3. Guru Pathik
The spiritual arts are not at their core concerned with combat ability, and some masters are never even seen fighting at all. Guru Pathik is the most notable figure, a spiritual advisor who mysteriously showed up just when Aang needed his help to master the Avatar State. Very little is known about Pathik, with his heritage, background and ultimate fate all left as a big, fat question mark. But what's not in doubt is his expertise.
Before he even met Aang, Pathik could sense the spiritual turmoil within Appa, communicating with the animal during his most frightened and vulnerable time. He felt the lines of energy within Appa just as he did with Aang and even came pretty darn close to helping Aang to master the Avatar State a season early. The fact that he was wrong about Aang forever locking himself away from accessing the Avatar State dings some points off Pathik's score, however.
2. Iroh
Everybody's favorite uncle had a whole lot going for him. On top of being a fountain of sage advice, a skilled martial artist, and a strong contender for the most powerful Firebender in Avatar, Iroh was also one of the most spiritually-attuned individuals hands down. He could see beings others were blind to, understood the importance of the world's spiritual balance, and even visited the Spirit World often throughout his lifetime.
What's perhaps most impressive is his transcendence of the boundaries of life itself. Some humans languished for eternity in the Fog of Lost Souls and fewer still could transcend into becoming spirits like the Painted Lady, but Iroh went a step further and preserved his spirit on his own power for an afterlife of bliss. He has tea parties, plays Pai Sho and even offers Korra advice that helps her improve the human world. What could demonstrate more spiritual mastery than that?
1. Zaheer
It turns out that Zaheer may be the only individual more spiritually attuned than Iroh. Though it's unknown whether Zaheer could also transcend life as Iroh did, the one-of-a-kind tricks Zaheer pulls off during his life shows a level of mastery unprecedented in the Avatar world. It was this mastery of his inner self that allowed him to "enter the void" and rediscover levitation after centuries of others believing the skill to be only a myth -- and that's just what Zaheer could do in the material world.
In the Spirit World, Zaheer could appear wherever he desired and could even pull other spirits to him and toss them off into the Fog of Lost Souls. He frequently visited the Spirit World through meditation and even maintained the ability to communicate with those in the physical world while he did so. Zaheer's spiritual mastery means that even in prison he is free, and he spends much the rest of his existence levitating in place as his spirit transcends his material bounds.