Rasengan in Naruto is quite an iconic and powerful technique. It's been used by multiple people and isn't one to mess around with.
The technique is challenging to learn, involving focusing chakra to a single point and swirling it around in a ball in the palm. Several higher-ranked ninjas and the godlike Otsutsuki clan are the only ones to have mastered it thus far.
Note: This list mainly ranks people's familiarity and skill with the Rasengan technique. It is also only the author's opinion.
Ranking the Rasengan users in Naruto
It was clear throughout Naruto that Kakashi never perfected the Rasengan technique himself. Instead, he modified it and created the Chidori technique.
There's not much to say there other than that he offers pointers to Naruto and later Boruto, as Rasengan is a technique that requires tons of chakra control not only to be used but also combined with their nature. While he can use all of the different nature releases, he favors lightning heavily.
Despite barely being able to manifest the technique himself, he does offer more than a few bits of advice on chakra control management.
The son of the Third Hokage has had better luck managing the technique than Kakashi has. Even as a genin, he could disrupt and kill one of Pain's bodies.
The only problem is, despite his excellent technique and Wind Release style being put into the Rasengan, his finesse and power with it are dwarfed by everyone else on this list. He's more than able to stand his ground with it, but it's the power difference that ultimately puts him this low.
6) Hiruko (missing nin)
The antagonist of the movie Naruto Shippuden: The Will of Fire, Hiruko was chiefly able to absorb many abilities within himself using what he dubbed the "chimera technique." It is rather horrifying as it involves absorbing his victims and their chakra until they are nothing but husks.
He gained the Rasengan technique by absorbing it from Naruto and was able to recreate the giant version of it. Yet, for all his power, Naruto's Rasenshuriken Rasengan was able to kill him.
Hiruko couldn't absorb it due to its complex shape (it was literally shaped like a pinwheel shuriken) and the nature of the attack itself as it has countless microscopic blades made of wind sawing through the target.
As a clone of Jiraya, Koji was able to summon Rasengans of various sizes, including ultra-big ones and larger ones that bested Konahamaru's own. His whole thing was stopping Isshiki Otsutsuki, but he also managed to best the new Team 7 with nary an effort.
He also managed to heavily injure his target with an Ultra Big Rasengan, so there's that.
The Legendary Sanin Jiraya is quite the teacher. While he didn't invent the technique, he learned from Minato and helped refine it. He was powerful enough to get a two-handed Rasengan without slowing down.
He was comparable to Minato with the Rasengan, using the Big Ball version numerous times. Having access to Sage Mode also helped create the Ultra Ball Rasengan.
He was able to use it to battle all six of Pain's paths and aid in the defeat of Urashiki Otsutsuki.
Naruto's son, Boruto, has shown quite some mastery over the technique. Not only is he able to spawn multiple versions, including some of his own like the compression Rasengan, but he's infused it with multiple natures and throw it as well.
He's also managed to perform more than a few complex feats with his Rasengan, including turning it invisible and making it huge with a bit of his father's chakra.
The X factor of the kama also means he can make the Parent and Child Rasengan or something comparable. The only problem with the kama is that he's possessed by Momoshiki Otsutsuki, which overrides his persona and will.
Minato Namikaze, aka the Fourth Hokage, invented the technique. He did so by witnessing and studying how the Tailed Beast ball worked for three years.
It required no hand seals and allowed him to instantly form and make it Big Ball size almost immediately. Combined with Flash-like speeds, he could wipe out 1,000 ninjas singlehandedly and even stop Obito and Kurama from destroying Konoha.
He could also access Sage Mode and had his own version of the Tailed Beast state, which significantly increased the power of his Rasengan too.
Of course, the series' titular character is number one. Why? Simply put, Naruto was not only the first to master the technique but the first to change it up. Rasenshuriken, Big and Ultra Ball, Father and Son Rasengan? All Naruto's. Heck, Sage Mode and Rasengan combinations were also him.
Naruto hasn't lost any steps as a result of this either. Even as Hokage continues to stand his ground time after time with the Rasengan and all manner of different styles, he also mastered Sage Mode to add to his Rasengan, something not even Jiraya could do.