Krillin had past training at another dojo but he was always denied respect because of his size. Krillin decided he was going to find the famous martial artist Master Roshi. Under Master Roshi, Krillin learned discpline Respect and that martial arts was not about being cocky and always being the best or the fastest. He was taught alongside Goku. After training with Master Roshi, Krillin was ready to compete in the martial arts Tournament. This involved the greatest fighters from all around the world. By Krillin's surprise he got further than most would believe.
Major Story Arcs
After Raditz was killed, Krillin and the other Z-Fighters learned that two more Saiyans Nappa and Prince Vegeta would be arriving to Earth in about one year and would be even more powerful than Raditz. So Krillin and the other Z-Fighters trained intensively at Kami's Lookout for the whole year in preparation. At the end of his training, Krillin would become far more powerful than Raditz.
Once finally arriving at Earth, Krillin helped stalling time for Goku by besting 3 Saibamen in revenge for Yamcha's death, and held off Nappa in various intervals. Unfortunately, Nappa was too powerful for Krillin and the other Z-Fighters. After a wished back Goku arrived at the battlefield, Goku easily defeated Nappa and would battle Vegeta after healing Gohan and Krillin with Senzu Beans.
After a long battle, Vegeta was eventually bested by the combined efforts of Krillin, Goku, Yajirobe and Gohan. With his pride heavily embarrassed, a battered Vegeta tried to crawl to his spaceship to escape and eventually seek revenge. Despite being heavily injured himself, Krillin managed to be to only remaining Z-Fighter able to stand. As Krillin noticed Vegeta attempting to escape, he took hold of Yajirobe's sword and was ready to avenge his fallen friends.
However, just when Krillin was ready to deliver the killing blow to Vegeta, Goku telepathically told him to spare his enemy's life. Goku's reasoning was to rechallenge him for the thrill of fighting as well as possibly allowing Vegeta to turn over a new leaf. Krillin is understandably skeptical over Goku's compassion for the man who almost destroyed the planet and scoffs at the idea that Vegeta is capable of turning over a new leaf, but he ultimately and reluctantly decides to trust Goku's judgment and lets Vegeta escape.
Krillin, Gohan,and Bulma went to planet Namek to find the Dragonballs, to wish the others that Nappa killed back to life. On Namek, they realized they were not the only ones looking for the balls. Also looking for them were Vegeta and Freeza, a very powerful and vicious tyrant. Worried of Freeza, Krillin and Gohan teamed with Vegeta to battle Feeza's evil henchmen, the Ginyu Force. Recoome, of the Ginyu Force, easily defeated Krillin, Gohan,and Vegeta. Once again Goku showed up to save Krillin and the others.
While searching for the Dragonballs, Grand Elder Guru unlocked Krillin's hidden powers. This was enough to keep him alive in battle with the Ginyu Force before Goku arrived. Unfortunately, Goku was unable to save Krillin from Frieza who eventually killed Krillin by blowing him to pieces telepathically. Krillin was later wished back to life with the Namekian Dragonballs.
Krillin was given a remote to shut down the androids, but could not kill Android 18 because he had a crush on her. After Cell was killed, Android 18 turned good and Krillin eventually married her.
Majin Buu Saga
Krillin and the other Z-Fighters went with the Supreme Kai to battle the evil wizard Babidi. However, Krillin was turned to stone by Babidi's demon lord Dabura who utilized a spit attack. Fortunately Krillin was turned back to normal when Dabura was killed by Majin Buu.
Eventually, Krillin was later killed by Super Buu at Kami's Lookout after being turned into chocolate and eaten offscreen. When Krillin was soon revived by the Namekian Dragonballs, he played a role in Kid Buu's defeat by lifting his hands to contribute energy for Goku's Super Spirit Bomb.
Krillin and Android 18 meet Android 17 while they were walking. Krillin tells Android 18 to fight Android 17's control, but is attacked by Android 17. Krillin is killed by Android 17 by a beam blast, where he was shot through the chest area. He falls to the ground and dies instantly from the attack. Android 18 attacks Android 17, but is easily defeated by Android 17 from a single beam struggle. Android 18 crawls to Krillin and knows that Krillin is dead. At the end of GT, Krillin is said goodbye to by Goku at the Kame House.
Krillin is seen as one of the people going to Baby's new world that he created. He leaves to the planet with his family and is one of the controlled people under Baby.
Power and Abilities
Although small, Krillin is considerably the most powerful human on Earth, with perhaps the exception of Tien. On Namek, his power level was over 10,000 - almost as strong as Goku during his fight with Vegeta (without Kaio-Ken).
Superhuman Strength: Krillin has always had superhuman strength since his appearance on Dragonball. At the end of DBZ, Krillin can easily lift about 75 tons.
Superhuman Speed : Krillin can fly at about Mach 4 by the end of DBZ.
Superhuman Agility: Krillin is many times more agile than a normal human. He has reflexes many times faster than a human.
Destructo Disk - Krillin's signature move where he forms a thin, flat, yellow energy disk that can cut through opponents easily. It is dangerous to opponents even more powerful than Krillin as Nappa had to dodge it and he cut off Freeza's tail with the attack.
Flight - Krillin can fly under his own power
Homing Energy Wave - Used against Piccolo in the 23 World Martial Arts Tournament. Krillin fires two deep orange energy blasts that home in on and track a target.
Kaio-Ken Technique - A video game only power. Krillin learns this move from Goku after he has died to train Krillin as Earth's protector.
Kamehameha Wave - The signature move of the turtle school. Krillin can fire a blue energy wave from his palms after saying the name of the attack. Krillin is on such a level where, unless he holds back, a full powered Kamehameha would destroy Earth easily.
Scattering Bullet - A large yellow energy blast that splits into multiple homing attacks meant to take out a large number of enemies at once. Krillin used this against the Saibamen and killed all but one of them.
Solar Flare - Learned from Tien, Krillin is able to shine a bright light into his enemies eyes to temporarily blind them.
Spirit Bomb - During the first battle with Vegeta, Krillin had th throw the Spirit Bomb since Goku was to weak to at the time. As a video game only move Krillin learns to perform the move after Goku teaches it to him.
Tri-Form Technique - Used during the fight with Nappa, this move can be considered a less refined version of Tien's multiple form technique. Krillin can split his being into 3 seperate entities to overwhelm an opponent through sheer numbers. This attack though splits his strength and energy between the three beings.
In the timeline where Goku died of a heart virus and the Z-Fighters never learned of the eventual attack of the Androids, Krillin was killed during the battle. He was one of the last Z-Fighters to die and was killed via a finger energy beam by both Android 17 and Android 18. Gohan was the only survivor and he would eventually train Future Trunks.