Krillin

Krillin (クリリン, Kuririn) is a supporting protagonist in theDragon Ball manga, and the anime series Dragon Ball, Dragon Ball Z, Dragon Ball GT and Dragon Ball Super. Krillin had a brief rivalry with Goku when they first met and trained under Master Roshi, but they quickly became lifelong best friends. Krillin is one of the most powerful and talented Human martial artists on Earth, Krillin is courageous, a faithful ally and good-natured. He is a prominent Z Fighter, despite usually being overpowered by the major enemies. His short stature and baldness (with the exception of when he grows out his hair in the Majin Buu Saga onwards) aid him in his ability to provide comic relief during tense moments. During the latter half of Dragon Ball Z, he largely retires from fighting, opting to settle down with his family instead, becoming the husband of Android 18 and the father of Marron. He has a Blood Type of A.[9]- Credits to dragonball.wikia.com

Later, Krillin gets back into training after Goku leaves at the end of Dragonball GT.

______                                                                                           Krillin has become famous because of his losing streak, but he started to train harder than ever because if one day someone would attack the Earth, Goku wouldn't be there to save them. After five years of training, Krillin discovered the Human Hidden Power, an incredible power sealed in every human or half-human after having trained and meditated a LOT. This power makes a human as strong as a full powered Super Saiyan 2. Only Krillin, Marron and Android 18 have unlocked this power. Master Roshi's Max Power is a similar weaker transformation.

___

One day Krillin found Gohan 's helmet from the time he played as the '''Great Saiyaman. 18 wanted Krillin to become Earth's new superhero (together with Mr.Satan, '''of course)

From that moment Krillin named himself: "The Kriller"                        The Kriller looks almost the same like Krillin and everyone in Krillin's city knows it is Krillin.