Sokka's boomerang was given to him by his father Hakoda before he left to fight in the Hundred Year War with the warriors of the Southern Water Tribe. It was one of Sokka's most prized possessions, and after losing it for a brief period of time, he considered it to be like losing a part of [his] identity. Sokka was particularly skilled with his boomerang, and frequently used it to hit enemies from a distance.
Though Sokka generally kept his boomerang with him at all times, he lost it after the Rough Rhinos attacked Team Avatar while they were sleeping. Sokka was bitter about its loss, but he managed to get it back when he defeated Yeh-Lu, who had taken the boomerang.
Sokka's boomerang played a crucial role in the defeat of Combustion Man, as no other member of the group could get within range of him without risking harm. The group was hiding behind a pylon, when Sokka threw his boomerang, which hit Combustion Man on his third-eye tattoo. This blow stunned the assassin and blocked his flow of chi to his third eye. When Combustion Man tried to firebend again, he blew himself up due to his blocked chi energy.
While knocking out two firebenders during the passing of Sozin's Comet in 100 AG, Sokka was forced to drop his boomerang and sword to save his and Toph's life.
A year later, Sokka had come to possess a boomerang again and used it to incapacitate a demonstrator outside Yu Dao whom he deemed annoying. He also used this same boomerang to demonstrate his authority to the newly released Princess Azula just before they and Zuko departed to search for Ursa, only to have it zapped clean out of his hand by the princess.
During Bending Supremacist Uprising, in the final confrontation, Sokka used his boomerang to knock out Yaling while she was fighting Toph, effectively putting an end to their duel.
Forty-two years prior to Avatar Korra's arrival in Republic City, Sokka mentioned his boomerang during Yakone's trial at City Hall, in which he referred to it as his trusty boomerang, and told the story of how he used it to defeat Combustion Man.