King Bumi is the king of Omashu. As a child, Bumi was a close friend of Aang, and is the only person who knew him before The War that is known to be still alive. He has become an old and eccentric man, prone to cackling laughter at unfunny jokes. Despite his age and his apparent frailty, Bumi is an Earthbending master, himself claiming at one point to be "the most powerful Earthbender you'll ever see".
Bumi's eccentricity arises out of the fact that he always keeps his mind "open to the possibilities". As a child, Bumi decided to use the Omashu mail delivery system as a chute ride, for which Aang dubbed him "a mad genius", a name that Bumi seems to appreciate. Although Bumi seems senile, he is in fact a brilliant and patient tactician, willing to wait until the opportune moment to strike to best effect. Bumi acts the same during a quiet, peaceful meal as he does when his city is under attack, and he rarely explains his actions, which tends to infuriate his underlings.
Bumi is the only one of Aang's childhood friends who has survived the 100 years in which Aang was stuck in the iceberg.
In "The King of Omashu", Aang returned to Omashu in order to show his friends Sokka and Katara the mail delivery system (in particular, they wished to use it as a slide). After accidentally destroying a cartload of cabbages belonging to the Cabbage Merchant, they were arrested and brought before King Bumi. However, Aang did not recognize his old friend, who was now 100 years older than when they last met. When asked what their punishment should be, Bumi told his guards to "throw them... a feast!"
During the feast, Bumi tricked Aang into Airbending, demonstrating that he was the Avatar. Now refusing to let them leave, Bumi demanded that the three be taken to "the newly refurbished room that was once bad" - in fact a comfortable sleeping chamber. After a relaxing night's sleep, Aang woke up to find his friends gone. King Bumi blackmails Aang into completing three tasks for him, or Sokka and Katara will be encased in Jennomite.
Aang successfully completed the first two tests (collecting a key from inside a waterfall and finding Bumi's pet Flopsie). The King instructed Aang to choose an opponent to duel as the final test. The King presented two different opponents for Aang to choose from, both formidable-looking in their own respects, and told Aang to "point to your opponent." Aang pointed to the apparently frail King, but quickly realized his mistake when Bumi threw off his robes and flexed his muscles, revealing himself to be a powerful and muscular Earthbender. Although Bumi had the upper hand during the fight, particularly against the run-and-evade tactics typical of Airbenders, Aang eventually impressed the old man by creating a tornado to counter a powerful attack from the Earthbender. Although Aang seemed to have Bumi in a corner after this, ready to strike with his staff, what he failed to notice was that Bumi had summoned a large mound of rock a few feet above Aang's head. Bumi however, was satisfied with Aang's performance, and allowed the match to be called a draw.
However, before releasing Sokka and Katara, the King demanded that Aang guess his name, and gives him a few minutes to think on it. At first, Aang is clueless, but as he thinks about the challenges he realizes that each one was designed to make him think differently than he normally would, and he solves the riddle with the words "Bumi, you're a mad genius". Bumi explained to Aang that strength and bending alone would not be enough to defeat the Fire Lord, and that when it came time for Aang to face him, "I hope you will think like a mad genius." After Bumi freed Aang's friends from the Jennomite (in fact made of edible rock candy), Aang and Bumi spent an enjoyable day using the Omashu mail delivery system as a chute ride, just like old times. Aang and his friends then left Omashu to continue their journey.
Aang, Katara, and Sokka returned to Omashu in "Return to Omashu", hoping that Bumi would act as Aang's Earthbending teacher. However, the group found that the city had been taken over by the Fire Nation. After helping Omashu's citizens and army to escape their imprisonment within the city, Aang attempted to free Bumi as well. After a chase down the city's large mail-delivery chutes, Aang and Bumi managed to escape a pursuing Azula. However, Bumi disappointed Aang with the statement that he could not leave Omashu just yet, as he was waiting for the proper time to strike against the Fire Nation from within, revealing that he, despite the metal cage he was kept in, was still capable of bending. Bumi advised Aang to seek an instructor skilled in neutral jing, or doing nothing (as Bumi himself put it, someone who "waits, and listens.") It was this advice that eventually led Aang to accept Toph as his Earthbending instructor.
Bumi would spend several weeks imprisoned in his city, waiting for the right moment to escape. That moment came on the Day of Black Sun. Taking advantage of the Firebender's loss of power, he broke out of his prison by Earthbending with his face, single-handedly liberated Omashu and even destroyed Ozai's statue at the top of the city in minutes. He later joined the Order of the White Lotus at Ba Sing Se.
Before the arrival of Sozin's Comet, Bumi met with the Avatar's gang again at Ba Sing Se, along with Master Pakku, Piandao, and Jeong Jeong, and is revealed to be a member of the Order of the White Lotus. Bumi is the only one to notice that the group is missing a "very important member", (as Aang and Momo have disappeared), but comically asks the group where Momo is. He then states that as long as Momo and Aang are together, they have nothing to worry about.
He joined in the Order's successful liberation of Ba Sing Se in the name of the Earth Kingdom, using impressive displays of his Earthbending to destroy many Fire Nation tanks. He presumably returned to Omashu after the war.
Bumi is an extremely powerful Earthbender, one of the best in the world of Avatar. In "The King of Omashu" he levitates extremely large stones during his duel with Aang, one being the size of a bus. He also performs the ability of bending Jennomite (rock candy). In Return to Omashu, Bumi also shows he is able to use his head to Earthbend by deflecting a fire disk shot by Azula and knocking her of the cart she used to pursue them in. He could also draw rocks towards him by using only the muscles on his face.
On the Day of Black Sun, Bumi single handedly liberates all of Omashu, taking advantage of the Fire Nation soldier's loss of Firebending. He uses his Earthbending to destroy the metal bridge connecting to Omashu, and vandalizes the statue of Ozai with a happy face and topples it. During the Battle of Ba Sing Se, Bumi, along with the other members of the Order of the White Lotus, liberate the city of Ba Sing Se. Bumi bravely takes on at least a dozen tanks with comet enhanced benders inside of them, and defeats them all, causing them to be stacked into a straight pile.
- The name "Bumi" means "Earth" in Indonesian and the Malay language, which is in turn derived from the Hindi or Sanskrit "Bhumi", meaning "Earth". However, since the word bumi with that exact meaning does not exist in Chinese, the negotiation letter in Return to Omashu had his name transliterated as 布米 (bù mǐ) which translate as 'to spread rice.'
- Bumi's voice actor, André Sogliuzzo, also plays Hakoda.
- Bumi is one of the few people who live throughout the entire war, since he knew Aang before he was in the iceberg. He is the second oldest living man in their world for being 112 years old, after Guru Pathik, who's 150 years old.
- Although Bumi tells Aang that he'll see him when the time is right, Aang never meets Bumi again during the series. They most likely met again off-screen after the war.