Galvatron is a reformatted Megatron, leader of the Decepticons. He battled the Mechanical Maniacs in their early days,
Galvatron is a madman, pure and simple. He remembers his former success as Megatron and can't help but rage against it, especially when the Mechanical Maniacs start beating him
Galvatron has a wrist-mounted fusion cannon capable of massive damage. He cam transform into a cannon to cause even more damage. Furthermore he's gigantic ... the Mechs fight him in mainly offbeat epilogues accounting for their victory against this overpowering foe.
Galvatron was mainly used in the offbeat early epilogues of the Mechanical Maniacs.
Before meeting them, he was banished from the Decepticons for his many failures and began to turn to absurd plots. He would meet Shadowman (Gauntlet) on some of these adventures out of pure chance (although he was convinced the ninja was stalking him). Galvatron would turn to the robot masters from Megaman 3 PC and would help them form the Sinister Six; giving them alternate modes based off various Megatrons in the Transformers series (although he would take these forms back after the Six's repeated failures). Eventually Galvatron would summon Unicron to Earth to feed the planet to his master, but the Mechs would stop this plan too.
Galvatron would join several other TV characters of his era in a team called the Legion of Doom, which mainly succeeded only in annoying the Mechs before they broke up thanks to Krang discovering Mother Brain and Mumm-ra's Alzheimer's being cured and wreaking vengeance on the team for using him while his mind was addled.
With the Mechs away in the first half of Series 4 the Decepticons, now under Galvatron, would start succeeding in world conquest. When the Mechs return and beat a few Decepticon plots, the Decepticons would work behind the scenes to capture the remnants of dying teams to aid in their plans. Viral Infection's villain the Death Virus and the Robotic Raiders villain Evil-Energy-Infected Duo are combined to give them the ability to possess all the robots on earth.
It's revealed that the power behind the Decepticon resurgence is a Unicron-reformatted Bizarro Shadowman under the even more behind-the-scenes Unicron. The Decepticons and Bizarro would all be defeated and Optimus Prime (whom the Decepticons were holding hostage and would later corrupt with Evil Energy) would taken them all away never to be seen again. Except for a cameo appearance in early Series 6 where he would be seen to have escaped and taking therapy, but still be even more delusional than even.