Megatron is a character from the Transformers

Transformers

A transformer is a device that transfers electrical energy from one circuit to another by magnetic coupling.Transformer may also refer to:* ASUS Eee Pad Transformer, an Android 3.2 Honeycomb tablet computer manufacturer by Asus...

 franchise, created by toy companies Hasbro and Takara. He is the primary antagonist and leader of the "evil" faction (primarily the Decepticon

Decepticon

The Decepticons are usually depicted as the antagonists in the fictional universes of the Transformers stoyline and related comics and cartoons, and the enemies of the Autobots and the University of California Davis Aggies...

s) in most of the various Transformers universes

Transformers universes

is an entertainment franchise. It began with the Hasbro Transformers toy line, centered on two factions of warring alien robots which are called the Autobots and the Decepticons...

.
Bob Budiansky

Bob Budiansky

Bob Budiansky is an American comic book writer, editor, and penciller, best known for his work on Marvel's Transformers comic. He also created the Marvel character Sleepwalker and wrote all 33 issues of that comic.-Career:...

, the writer for the Marvel Comics series, stated that originally Hasbro took issue with the name, saying it sounded too frightening

TNT equivalent

TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

. Budiansky responded that as the lead villain, that was the point. Hasbro saw his reasoning, and approved the name.
Originally, Megatron was able to transform into a Walther P38, delivering more focused energy blasts.