From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Hirudegarn war is the name given to the conflict raged between the Konatsians and the Kashvar.
Main article: Dragon Ball Z: Wrath of the Dragon
The Konatsian warrior Tapion explains to Bulma that a race known as the Kashvar, power hungry aliens who believed themselves to be the superior beings in the universe, re-awakened an evil monster called Hirudegarn in an attempt to easily eliminate the population of Planet Konats. Centuries ago, ancient warrior Konatsians defeated the monster, but the Kashvar had found a way to resurrect the beast using dark magics. Over the course of the following year, Hirudegarn wiped out nearly half of the planet's population.
The enchanted items
It was not until a Conutsian Priest came upon an ancient enchanted sword and two magical Flutes that there was any hope for victory. These flutes were given to Tapion and his younger brother, Minotia, in hopes of using their melodies to distract Hirudegarn. The enchanted melodies worked and consumed the monster with a great amount of rage. While distracted, the priest drew the blade and cleaved Hirudegarn in two. Each half of the beast was then trapped within Minotia and Tapion. The brothers became heroes, but the Kashvar still sought them out and the two halves of Hirudegarn being near each other was dangerous. The Kami of Planet Conuts believed that the only option was to seal the two brothers inside enchanted Music Boxes and send them into the far reaches of space apart from each other. Unfortunately, at least one Kashvar still sought them out one thousand years later.
1000 years later
Main article: Wrath of the Dragon
Eventually, the last surviving member of the Kashvar, Hoi, found both of the music boxes. He managed to somehow open Minotia's box, and the lower half of the monster was released. Hirudegarn proceeded to kill Minotia, and Hoi took control. Hoi, then, proceeded to travel to Earth, in hopes of using the Dragon Balls to open Tapion's music box and free the top half of Hirudegarn. After tricking the Z Warriors, he successfully released Tapion. Later on, the Z Warriors battle Hirudegarn, who was fully released from Tapion's body and had merged together with the lower half. The monster, eventually, transforms into a new, more powerful form, where he is eventually finally killed by Super Saiyan 3 Goku's Dragon Fist attack. Tapion gives his sword to Trunks and uses Bulma's time machine to travel back to his own time.