Leonardo da Vinci led a pretty interesting life he was an inventor, painter, musician, mathematician, engineer, and about a million other things but the most important thing he did was help out Ezio Auditore de Firenze (in the world of Assassin's Creed, at least). Leonardo acts as the Q to Ezio's James Bond, creating and building him weapons and flying machines in the struggle against the Templars. And when Leonardo da Vinci is mentioned to a kid today, the only thing they'll know him from is Assassin's Creed, which is actually an improvement over the past few decades, when he was only known as a Ninja Turtle.
On Wander's lonely journey to kill a bunch of innocent giants, Agro is a welcome presence transporting you across vast stretches of land, occasionally taking part in a Colossus battle, and even sacrificing itself to save your life. There may not be another more tragic and heartbreaking moment than when Agro falls from the collapsing bridge. At least you're able to take a breath of relief at the end of the game, where it's revealed ol' Agro just hurt its leg a little, straight up dashing the hopes of glue factory owners everywhere.
War never changes, and neither does Dogmeat. One of the very few characters to carry over throughout the series, the always-too-eager to fight mutt has stood by the side of many ex-Vault Dwellers, Chosen Ones, and Couriers. And the true test of his worthiness as a sidekick is that Dogmeat would attack anyone, anywhere, for pretty much any reason, even when the enemy was 20x his size, wearing armor, and brandishing a plasma rifle. The wasteland could be a lonely place, so thank the NCR that you could always have this lovable pooch by your side. Until he died, that is. Which was often.
It's no wonder Falco's on this list he's the only member of the StarFox crew to be a wingman with actual wings! (ducks barrage of tomatoes) Anyways, Falco Lombardi is not your average sidekick he's got a rough exterior, he's always making sarcastic remarks at Fox (even when Fox is literally saving his life), and he's got a pretty sizable ego for someone who pretty much never is responsible for any of the team's accomplishments. Regardless, he's always there for the team, helping defeat the armies of a giant monkey head and his floating pair of hands, no matter what the cost. Also, he makes references to Einstein, meaning StarFox takes place in the same world as ours! When a sidekick can blow your mind like that, you know they're a keeper.
Kazooie puts up with a lot, living inside of a backpack worn by a shirtless bear and all, which makes it all the more amazing she remains such a steadfast and useful sidekick. She can fly, shoot eggs, peck mercilessly, and carry Banjo when he can't climb something. That's probably way better than anything you've ever carried in your backpack, even if you did have a really, really cool trapper keeper.