Megatron

Not to be confused with Metatron

Megatron (Later Galvatron) is the leader of the Decepticons, as well as a member of the Warsaw Pact when he was Megatron and is also the supreme boss and founder of the Supreme Golden Ace Invasion Organization (More info below) after becoming Galvatron.

He and the Teletubbies formerly hated each other since Megatron was a Communist, and the Teletubbies were Nazis

He transformed into a gun, but then a tank.

After he got DIEded by Optimus Prime, he was later revived and legally changed his name to Galvatron by one of his allies Chin-Chin (Who would later become one of the bosses of the Supreme Golden Ace Invasion Organization).

Eventually, he signed an agreement with the Teletubbies that let Bob Saget, the Decepticons and some other n00bs visit Poland whenever they wanted. He later gave them back the Eastern portion of Poland and decided to work together. Then, he founded the Supreme Golden Ace Invasion Organization.

As Galvatron, he had a new cannon mode, but then he became a jet because he hated being something that was non-vehicle.

He later encountered Thanos and joined his Infinity Army; he was the twenty-first member chronologically, but he after its collapse, he joined Kamen Rider Decade's new alliance, the Decade Alliance. He's more satisfied with the latter group than the former.

However, he was sent by Decade to kill The Twelve Homestuck Trolls. He failed to do so once, if he fails to kill all of them by June 2020, if not sooner, Decade would replace him with Shockwave; the latter has been loyal to Galvatron for years, but Shockwave was more powerful and dangerous than him. During one attempt to kill the Trolls, Galvatron came close to killing Nepeta Leijon when Dio Brando came in and fused with Galvatron to create the abomination of Gigatron.

On a side note, Megatron is also the star of Megatron sends Rath to Japan.

In the Real World, he actually serves the same master as Optimus Prime, Capitalism (which, obviously, is just another form of Mammon).