Tenzin is the son of the late Avatar Aang and Katara. He is the Air Bending master of his time.
After the Hundred's Year War that Avatar Aang helped to win, he settled down with the Water Bender Katara as the two married and had children. Tenzin was the youngest of three siblings with Kya, the oldest, and Bumi, the middle child. However, Tenzin was unique among his siblings as he was the only Air Bender that emerged. Working with his father in Republic City, he helped to build Air Temple Island where monks could be trained in the art of airbending. Growing up in Republic City, he was well acquanted with his father's friends, especially Lin Bei Fong who he had a relationship with before Pema confessed her love for him as he and Lin grew apart. After Aang passed away, Tenzin married Pema and had three children Jinora, Ikki, and Meelo, all of which became airbenders save for his wife. As the world's Airbending master, he holds high power in Republic City as he works to help build the legacy his father started. He came into contact with the next Avatar, Korra, through his mother as he agreed to train her once she was ready.
Tenzin was created by Bryan Konietzko and Michael Dante DiMartino for the new part of the Avatar franchise, The Legend of Korra. His role is that of the great masters that his father had while he trained to become the Avatar. His name comes from the 14th Dalai Lama, Tenzin Gyasto. He made his first appearance in Episode 1: Welcome to Republic City and is voiced by J.K. Simmons in the English version.
As the son of the late Avatar, Tenzin has upheld all the traditions and values that his father taught him as he grew up. While he understands the fundamentals of air bending, he is also a patient man who works hard to keep up the legacy his father left behind. This clashed time and time again with the hot temper of Korra, who would rather rush into a battle as opposed to working on the spiritual side of being the Avatar. Tenzin lives in the age of tradition and values that were around when his father was a child. He denounces several modern amenities and disapproves of various activities, including the sport of pro-bending which he sees as a mockery to the art of bending. Despite being a man of values, he is willing to admit his faults and when he is wrong. He is more of a surrogate father figure for Korra than a master at times, worrying about her well being physically and mentally above all else.
When Korra is found to be the Avatar, Tenzin is only in his early forties but promises to train Korra once she masters her other elements first. When Katara announces that Korra is ready, Tenzin brings his familiy to the South Pole as he expresses his regret to inform Korra that he cannot train her at the moment as there are too many problems going on in Republic City. Korra sneaks away to the capital anyway as she gets in trouble for vigilantism and destruction of property. Tenzin bails her out as he makes a deal with Lin that she'll head back to the South Pole. Korra detests it, saying that its her duty as the Avatar to learn the elements but she is unable to if the world's only airbending master can't train her. He realizes that she is right, as she is just as much of his father's legacy as is the city. He agrees that she can stay in Republic City on Air Temple Island.
However, the only stipulation is that she remains on the island under the watch of the Order of the White Lotus. Korra wants to see the city and watch pro-bending but Tenzin dennounces it, saying its a mockery. Korra is worried about airbending as he knows its hard for her to do it like how it was hard for Aang to earthbend. He tries to teach her several concepts but her brazen attitude gets the better of her. After a failed attempt to learn the stance, Korra blames Tenzin as a horrible teacher as Pema states that Korra needs space. In attempt to make amends, he looks for Korra but finds she is playing pro-bending as a waterbender for the Fire Ferrets. Angered, he tries to bring her back but leaves in frustration. Staying to watch, he sees how the sport helped her move like an airbender as the two apologize to one another. Soon after, the Equalists hold a massive rally where Amon shows himself to the public and displays his ability to energybend. Korra tells Tenzin of the discovery as he knows that the Equalists are a force to be reckoned with.
When Tenzin learns of the power of the Equalists, he attempts to convince the council to try and make peace but the Northern Water Tribe councilor Tarrlok wants to extinguish them instead. The vote is passed to make a task group as Tarrlok intrudes upon Tenzin's home, trying to get Korra to join. To both councilors surprise, she declines as she points the reason is because she wants to train in the bending arts. Tenzin senses something else is wrong as he tries to get her to open up but she sticks firm to her desires. At a gala held by Tarrlok in Korra's honor, he sees how the whole event was set up to goad Korra into joining the task force. However, when Korra challenges Amon to a duel, both councilors think it's a rash decision. After the Equalists ambush her, Tenzin comes to her aid as she confesses her fear of the group, breaking down as he comforts her.
Things go back to normal until Amon threatens to attack the Bending Arena during the final match of the Tournament unless they shut it down. Korra, Mako, and Bolin try to sway the council, but once again, Tarrlok and Tenzin agree that its for the best. Lin interjects, stating that they shouldn't succumb to fear as Tarrlok and the others switch their votes. Tenzin talks with Lin to give her a chance with Korra, stating that what happened between them shouldn't affect other people. During the match, Tenzin notices the cheating as he yells at the referees. What they don't see until the last minute are that the audience members are secretly Equalists and subdue him. Only after the attack and destruction caused by Amon and his men does Tenzin know they at war.
Investigating the attacks, Tenzin and Lin begin interogations while Korra looks for her own leads. Listening in on Hiroshi Sato telling someone about his ties, she brings the findings to the two. Tenzin realizes Hiroshi has the motive as his wife was killed by an Agni Kai gang member ten years ago. Telling the industrialist what they know, he invites them to search as his daughter, Asami Sato, and Mako verbally attack Korra and Tenzin. Finding nothing, they get a tip from a factory worker about a secret warehouse under Hiroshi's home. However, Tenzin and the others are overpowered by Hiroshi's new machines. Due to the intervention of Asami, Mako, and Bolin are they allowed to escape as Tenzin tries to convince Lin to stay Chief of Police; something she doesn't want to be as she wants to hunt Amon outside protections of the law.
When Saikhan becomes Chief of Police and announces how he will directly report to Tarrlok, both Tenzin and Korra declare it to be a foolish decision as he reminds Korra to try and synch with her spiritual side due to recent visions she has been receiving from Aang. After the new Team Avatar stops several Equalist attacks, Tarrlok pushes for new laws on non-benders as Tenzin opposes them more so than any of his other plans. Even after Asami, Bolin, and Mako are imprisoned, he urges Korra to remain patient which results in her getting captured by Tarrlok. When Tenzin receives the news though, it is said that the Equalists were behind it. Banding together with her friends and Lin, Tenzin goes underground to find an Equalist bunker and several captured metalbending police but no Korra. They approac h Tarrlok, knowing he was behind it as it is revealed he is a bloodbender. Tarrlok is able to knock the group out as Tenzin searches for Korra, who shows up in the middle of the night injured.
Korra tells the group about how Tarrlok was Yakone's son and that she was able to connect to her spiritual self when Tenzin leaves for a Council meeting, asking Lin to protect his family. Instead, he is almost ambushed as he is now the head of Republic City as all the other Councilors had been captured as the Equalists launch war on the city. Working together with Saikhan, they try to help but are captured once more by the Equalists. It is only thanks to Korra and her friends that he is freed but sees that Air Temple Island is under attack. Rushing home, he chastises Lin for allowing his children to fight but is happy to see they are safe as well as his new son, Rohan. Korra reminds him of the war as Tenzin plans to take his family to safety then return, demanding Korra go underground until Iroh comes with the United Forces. Lin comes with them, knowing they are the last airbenders in the world and sacrifices herself to Amon to save them. Instead, Tenzin and his children are captured anyway as Amon plans to rid the world of airbending but Korra intervenes, telling Tenzin to save Pema and the children. After she defeats Amon at the cost of her bending, Tenzin brings Korra to his mother but Katara is unable to help. Tenzin waits, knowing she needs time as Korra finally meets the spirit of Aang, unlocking the Avatar State and the art of energybending with it as Tenzin admires her with pride.
As the son of the Avatar, Tenzin learned everything he knows about airbending from his father. He learned the fundamentals, stances, and techniques that his father learned and invented himself. Because of this knowledge, he is the only Air Bending master in the world, evidence by his tattoos. Luckily, he is able to pass on the knowledge of the almost lost art to his children and the next Avatar herself.