Goku's True Dragon Ball Legacy Is An Attack, Not Kamehameha
Of all the fighting skills and fighting styles that Goku displayed throughout Dragon Ball, there was one that would become his true legacy.

While Goku has no shortage of extremely effective techniques and chi blasts he uses in any fight of his Dragon Ball career, there is one that has proven time and time again to be his true legacy.
Goku made his debut in Dragon Ball Chapter 1, and since his debut, it's become clear that he's a force to be reckoned with. In the classic Dragon Ball franchise, Goku, who was still a child at the time, had already risen to fame as one of the most powerful fighters in existence. While Goku earns this title by traveling the world and stopping bad guys wherever he finds, two victories stand above the rest: Goku's victory over the Red Ribbon Army and King Piccolo - he defeated two villains (or villain entity) ) Exactly the same way he used to beat them is passed on to his children.
In Akira Toriyama's Dragon Ball Chapter 490, Gotenks is fighting Majin Buu after becoming the only warrior on the planet strong enough to stand up to the villains. At this point in the saga, Vegeta Goku is dead, and Gohan is presumed dead, so all responsibility for protecting the planet and stopping the deadliest threat the Z-Fighters could ever face falls on two kids less than 10 years old. However, what they lack in age or combat experience, Goten and Trunks make up for in strength - and they prove it in this chapter.
Gotenks Utilizes a Move Made Iconic By Goku

When fighting Majin Buu, Gotenks apparently had difficulty delivering effective blows. Even though Gotenks was the strongest warrior on Earth at this point, Majin Buu didn't seem to be hurt in any way. So, to hurt him, Gotenks threw his body at Majin Buu and smashed his own head into Buu's head, which proved to be enough to cause Buu pain. With this move - throwing himself first at an opponent with great effect - Goten (as Gotenks) carried on his father's legacy. Back in the canon days of Dragon Ball, when Goku was fighting the Red Ribbon Army, he first went through his mecha suit and killed the leader of the fascist group. Goku then did the same thing while fighting King Piccolo - flew head first through the villain's chest, killing him for a moment. When Gotenks lunges headlong at Buu, it's the first real attack against the villain, proving its effectiveness in combat - and Goten isn't the first kid Goku has used this attack on.
Early on in Dragon Ball Z, Gohan uses this "leading" attack on his uncle Raditz after the evil Saiyans kidnap him and threaten his father's life. Gohan nailed Raditz to the torso with his head, just like Goku did to General Black and King Piccolo of the Red Ribbon Army. When Gohan did this, he weakened Raditz enough to give Goku and Piccolo a much-needed advantage, resulting in the Z-Fighters winning. From Goku to Gohan and finally Goten, the astonishingly absurdly simple "first strike" attack somehow turns out to be one of the greatest attacks in Dragon Ball history - and it turns out to be Goku's true legacy .