Irko

Irko is the family ship between Iroh and Zuko from the Avatar: The Last Airbender fandom.

Canon
They are extremely close in canon, Iroh thinks of Zuko as his son and Zuko recognizes Iroh as being the one to be a true father to him. There are multiple instances where they save each other from getting hurt (ie. Iroh preventing Zhao from attacking Zuko, Zuko rescuing Iroh from the earthbenders, Iroh saving Zuko from Azula's lightning and etc.) Iroh has raised Zuko from when he was 13 to 16 and played a big part in what type of person Zuko turned out to be.

Book One: Water
Iroh was accompanying Zuko when he found Avatar Aang after his long search. He constantly supervised his firebending exercises and mentored him before his Agni Kai against Zhao. Zuko was always impatient in his search for the Avatar while Iroh attempted to calm him down and enjoy a cup of tea. He tried to talk Zuko out of chasing Aang into Fire Nation territory since was not to return. Zuko also chose to save his uncle from earthbenders who had captured him over chasing the Avatar.

Iroh spoke to Lieutenant Jee after the latter was irritated with Zuko's behavior towards his crew. Iroh explained Zuko's past to the lieutenant and the events that led to his exile from the Fire Nation. The lieutenant had believed that Zuko's scar was an accident but Iroh corrected him and stated that he witnessed the event which he could barely watch. He finally helped Jee see why capturing the avatar was so important to Zuko.

Zuko was later seemingly killed when pirates hired by Zhao set fire to his ship. Iroh knew that Zuko had really survived and pretended to join Zhao for the Siege of the North while allowing Zuko to infiltrate his ranks as a soldier. He also encouraged his nephew to get a head start on sneaking into the Northern Water Tribe so that he could capture the avatar before Zhao had a chance to.

Book Two: Earth
After the two left the North Pole, the tides brought them to the Earth Kingdom. Azula greeted them and said that Ozai was allowing them to return home. However, they soon realized that they were returning home as prisoners and became fugitives of the Fire Nation. Zuko had issues adapting to their new lifestyle and eventually decided to part ways with his uncle. Iroh was saddened by this but secretly followed Zuko from afar so that he could always be there for him.

Zuko and Iroh eventually reunited against Azula on the battlefield. Azula shot Iroh with lightning which caused great distress in Zuko but his uncle eventually recovered from his injuries. He taught Zuko how to redirect lightning in order to combat his sister. They eventually made their way to Ba Sing Se as refugees. Zuko did not wish to start a life there while Iroh became involved in the tea shop business.

Zuko had issues with adapting to his new life in Ba Sing Se and letting go of hope with returning to the Fire Nation. He attempted to capture Appa in order to get to Aang but Iroh stopped him by pointing out that there was still no way for him to be redeemed in the eyes of the Fire Nation at this point. Zuko fell ill after releasing Appa and Iroh cared for him until he recovered. Zuko was finally happy with his life after he recovered and enjoyed helping Iroh in his tea shop.

Zuko was eventually captured by the Dai Li after Azula and her team infiltrated Ba Sing Se. Iroh went to rescue his nephew along with Aang. Iroh battled against Azula in order to help the avatar but Zuko was still conflicted. After Azula promised him redemption, Zuko finally turned against his uncle and attacked Avatar Aang. Iroh was taken prisoner and clearly hurt by his nephew's behavior. Zuko lamented that he betrayed his uncle but his sister argued that Iroh had betrayed him.

Book Three: Fire
Zuko returned to the Fire Nation and was welcomed back by the Fire Lord while Iroh was imprisoned. After realizing that Aang was still alive, he visited his uncle in prison and asked for advice on what he should do. Iroh turned away from him and did not speak at all. This angered Zuko who then told him to waste away in his cell. Iroh continued to remain silent every time Zuko visited him in prison.

Iroh finally sent Zuko a letter to learn about his past and revealed to him that his maternal great-grandfather was Avatar Roku and gave the headpiece of the crowned prince that Sozin gave to Roku. Zuko later decided to rejoin Team Avatar on the Day of Black Sun and went to bust Iroh out of prison but found that he had already escaped. Zuko then confronted his father Ozai and told him that Iroh was more a father to him than he was.

Zuko joined Team Avatar but had trouble getting the members of the team to trust him. He sought imaginary advice based on what he thought his uncle would say and tried to serve tea and tell jokes like Iroh but could not remember the whole joke. Zuko still felt immense guilt over betraying Iroh. This was shown when Team Avatar attended a play about themselves and Zuko stated that he might as well have stated those awful things that the actor portraying him said.

Zuko sought out Iroh when Sozin's Comet was approaching and Aang was missing by having a Shirshu track his scent with one of his sandals. He was nervous when reuniting with his uncle and broke down as soon as he arrived. Iroh turned around and embraced Zuko, saying that he was just worried he had lost his way but was proud of him for finally joining Team Avatar. Zuko wanted Iroh to take town Ozai and become the Fire Lord but Iroh told Zuko that defeating Ozai was Aang's job and that Zuko was destined to become the next Fire Lord.

The Legend of Korra
Years later as it leads to the Legend of Korra timeline, Iroh had passed away but his legacy and memory live on. Zuko's daughter had named one of her sons after Iroh, who became a general like he was. Korra later journeyed to the Spirit World and asked Uncle Iroh for advice when she failed to ambush Zaheer. He suggested that she seek out Zuko for advice. Korra did so and he was surprised to hear that she spoke with his uncle in the Spirit World.

Fanon
Though it's well established that Iroh is the father Zuko never had and Zuko is the son Iroh lost there are some fans who ship them romantically. Most though just recognize their father - son bond. When Iroh was revealed to have ascended to the Spirit World permanently in The Legend of Korra, many fans wanted Zuko to reunite with his uncle in the Spirit World and some fanart has been drawn where the two reunite.

Fandom
FAN FICTION

Trivia

 * There isn't as much Iroh adopting Zuko fanfiction as you'd expect considering how close they are in the show and how most fans adore the relationship.
 * If you search up who Zuko's father, Iroh appears (along with Ozai) in the results although they are not "officially" father-son in canon.
 * Some fans like to theorize that Zuko's daughter, Izumi, calls Iroh grandfather.
 * Even before his son's death, Iroh has shown to be very close to Zuko.