Sokka is a fan-favorite character in Avatar: The Last Airbender. While he is considered to be the comic relief member of the Gaang and has a lot of goofy moments, there's no doubt that he's the smartest member of the team. As a non-bender, he must rely on his wits and tactical skill in order to hold his own against benders.
Because of this, he becomes the member of the team that always comes up with the plans, and he has amazing out-of-the-box ideas. Over the course of the show, viewers see him grow in confidence and he ultimately realizes that his mind is his greatest weapon, which leads to a lot of his smartest moments.
When He Told The Northern Water Tribe About The Fire Nation
Sokka has managed to pick up a lot of knowledge about the Fire Nation during his travels, and this makes him a valuable person to the Northern Water Tribe's army. When Han smugly tries to claim that the Fire Nation's uniforms and tactics look a certain way, Sokka is easily able to refute those claims, because he knows better.
This leads to the Chief of the Northern Tribe recognizing his brain and making him the leading member of the mission that he has been assigned to. He then asks Sokka to protect his daughter, Yue, as he truly believes that Sokka is the most capable person to do that.
When He Comes Up With An Escape Plan
Escaping the Boiling Rock is supposedly impossible, but not for Sokka. He and Zuko are only there for a few days and he manages to come up with a plan that will be able to withstand the harsh conditions of the prison. They execute an elaborate scheme of Zuko getting thrown in the cooler so that he and Sokka, who is cleverly posing as a guard, can later steal that cooler to float across the prison's boiling moat.
While Sokka and Zuko didn't end up using that plan, and the convicts who did messed the plan up, it was still a genius idea, as expected from Sokka. It's definitely why this episode is one of Sokka's best.
When He Plans An Airship Slice
During the final battle in the series, Sokka, Toph, and Suki are trying to figure out how to take down a whole fleet of Fire Nation airships. It seems like a difficult feat, but then Sokka figures out a plan, which he aptly names "Airship Slice!"
The plan is fairly simple; he simply flies the ship they have hijacked and crashes it across the roofs of all the other airships. It works, and the fleet is destroyed. Sokka's skill is often being able to see an obvious idea that others can't, and this moment is a great example of that. Thanks to him, the Earth Kingdom isn't burned down completely.
When He Made Everyone Pretend To Have Pentapox
When Omashu is taken over by the Fire Nation, any attempts of rebellion are stifled, and it seems that there is no way for the city's inhabitants to escape. Enter Sokka and his brilliant mind.
After receiving some sucker marks on his face from a purple pentapus, which he pretends to be marks of the deadly disease pentapox, Sokka encourages everyone in Omashu to pretend to have the illness. He even guides a class on how to act ill. His plan works, and everyone manages to escape safely. Sokka's ideas may always be a little kooky, but that's what makes them so brilliant.
When He Invented The Hot Air Balloon
This is definitely one of the best things that Sokka ever did, as he created one of the biggest technological advances that the Avatar world ever sees: the hot air balloon. After becoming friends with an inventor in the Northern Air Temple, Sokka helps him figure out a way for people to fly, which ends up being the aforementioned invention. This genius idea helps save the temple from invading firebenders.
His invention was subsequently stolen by the Fire Nation, so this may be one of the times that Sokka's brains worked against him. But if a global superpower thinks that his ideas are good, then that definitely says something.
When He Figured Out How To Stop The Drill
When the Fire Nation's giant drill attacks Ba Sing Se, the city's military has no idea what to do. They can only think to throw rocks at it from the outside. Good thing that Sokka is there, as he has the idea to infiltrate the drill and take it down from the inside.
Not only that, he tricks an engineer into bringing them the plans that they use to coordinate their attack on the drill. Because of Sokka's brain, Ba Sing Se lives to fight another day. This is also the episode where he officially makes himself the "Plan Guy," so this episode is definitely a showcase of his smarts.
When He Defeated Sparky Sparky Boom Man
Sokka can officially say that he has defeated one of the deadliest firebenders out there, one that even Zuko or Aang couldn't defeat. When Sparky Sparky Boom Man attacks the Western Air Temple, Sokka figures out a way to fight back while remaining behind cover.
Sokka remembers how Toph managed to disarm him in an earlier episode, and fires his boomerang at Sparky Sparky Boom Man's head. His plan ultimately saves the day, as it causes their enemy to blow himself up. This event proves how Sokka is able to think on his feet, and how often Sokka's intelligence is a bigger strength and weapon than bending.
When He Fights Piandao
In the episode "Sokka's Master," Sokka is uncharacteristically feeling that he is not reaching his full potential. He learns how to sword fight from Piandao, and is more successful than Piandao's other students because he is much smarter. This is shown by how Sokka responds to the tests that Piandao gives him in clever and unusual ways.
When the two have a sword fight in the episode's climax, Sokka successfully uses all of the techniques that he has been taught, which his master heavily compliments. Sokka is a tactical foe, and while he doesn't win the fight, he earns Piandao's respect.
When He Evacuates The Village
The episode "Jet" is one where Sokka's brains are really showcased for the first time. Sokka's intelligence and instincts get questioned a lot in this episode, but he proves everyone wrong by ultimately saving the day.
When Jet blows up a damn in an attempt to kill everyone in a nearby village, the other heroes believe that stopping the bomb is the only way to save everyone. When they can't do that, they think that the village will perish. But Sokka instinctually realizes that the best plan is to evacuate the village. By thinking outside the box, everyone survives because of him.
When He Comes Up With The Day Of Black Sun Plan
When the Gaang is looking through the Spirit Library - which Sokka, ever the scholar, wants to go to for a vacation - for knowledge to defeat the Fire Nation, Sokka is the only one who succeeds in finding something. By using an ancient calendar, he is able to decipher multiple answers from a destroyed piece of paper that he finds, which shows just how resourceful he is.
He figures out how firebenders lose their power in a solar eclipse, and subsequently plans an attack on the Fire Nation that he leads in the third season. The Day of Black Sun arc is a great show of just how far Sokka has come in terms of brainpower.