Boomer

''Boomer is a Valkeryian Herald of Unicron from the Super Dion Bros series. ''

Boomer hails from another world. His involvement with the Energon War is because of the sudden destruction around Earth. He went on becoming a partner with Sideways and his little group that wanted to revive Unicron after the death of his loved one.

War For Energon: Boomer's Beginning comic
Somewhere on Earth, Boomer begane wondering why there was so much destruction around the world and why his friends were acting wierd. He ran into Shock when he was looking for Decepticons, and that's when Boomer saw the Decepticon Battleship and he flew after it...meeting Delgatron X for the first time. A small struggle of power happened between the two until Oni stepped in between the two blasts. The both of them got blasted into the Hydra Cannon Command Chamber and it appears that the cannon itself was damaged. Delgatron attacked Boomer again and the impact of the blast from Boomer made the cannon unstable even more and was about to explode, Delgatron retreated, the cannon exploded and Oni absorbed the explosion but got killed in the process.

Back on the deck of the ship, Boomer swore he would bring her back. Delgatron didn't worry about the Hydra Cannon being destroyed, saying he could build a new one. Boomer went back to his lab, sending away one of his creations, Zeon, while he had plans with another one he still had with him.

Delgatron X had his army ready, and sended out the leader to scan the Autobot and copy their abilities. Boomer however had other plans with this. He used Upgrade to take control of the Gizoid leader and self-destruct it above the Decepticon ship, also destroying the Gizoid army.

Later Boomer encountered Ancud, thinking Boomer was a Decepticon Ancud attacked him. He walked further and suddenly Sideways appeared. Sideways enraged Boomer by telling him what he'd lost and might never get back. Boomer exploded in rage and then got picked up by Upgrade.

On some power plant Sideways once again appeared before Boomer, this time in full body, convincing him to join Unicron and get the ultimate power. Boomer agreed on becoming part of Unicron's revival, and so he joined the Decepticons to spy on them.