Affiliation: Decepticon
Function: Decepticon Leader // Tyrant

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Alternate modes:
Cybertronian Star-Fighter Jet
Weapons: 

First cartoon appearance: Transformers Animated, intro movie, " Transform and Roll Out."

First Comic Appearance: Transformers Animated: Arrival #1

"The Allspark will be mine, and Cybertron will tremble at my eet."

Bibliography of significant appearances: In this form, with his Cybertronian Alternate mode, he made only a few appearances, most notably in the Transformers Animated movie introduction: Transform and Roll Out.  Of course, it was this form's decapitated head which featured so prominently in the series until his return with Earth mode helicopter. 

MEGATRON is a fierce, unyielding despot who sees himself as a freedom fighter. He sees the DECEPTICONS as an oppressed race suffering under the tyranny of the AUTOBOTS. The DECEPTICONS must survive by any means necessary. He takes extreme pleasure in the suffering of even a single Autobot. And MEGATRON does not care at all for the collateral damage known as humans who might happen to stand in his way. He has the zeal of a fanatic and demands the unquestioning loyalty of those who serve him. 

Robot Mode Power: MEGATRON begins the series with only one power: the power to lie and manipulate Sumdac to repair and reconstruct him. Over time, the MEGATRON head will develop into a powerful psychokinetic who can control any machine. While the Cybertronian minds are too advanced to succumb to this ability, MEGATRON can control virtually any robot on Earth and the automated plants that construct them. In addition to this power, MEGATRON’s eventual robot body will be equipped with an assortment of laser cannons, sonic missiles and pulse blasters. 

Vehicle Mode Appearance: Cybertronian Gunship. 

Character description from package "tech spec":  Back on Cybertron, when it's late at night, and very dark, robots tell each other stories of war.  they spin stories about the deeds of Megatron, and though robots don't feel cold, the listeners shiver.  The only ones who done enjoy a scary Megatron story are the old ones, the ones who were there.  Those old Autobtos remember the real Megatron.  Many of them bear scars sustained in the heat of his fusion cannon, or dents delivered by his powerful swords.  To those old robots, Megatron is no monster; he's a warrior so vicious and terrible that monsters pale in comparison

Galactic Powers and Abilities:
>  No known weaknesses.
> Scientific, strategic and engineering genius.
> Fusion cannon can disintegrate up to 40 feet of solid steel.

Other appearances: Take a deep breath because this could take awhile!  Whether you consider Animated Megatron to be connected to any of the previous incarnations or not, there is no disputing, there are few other persona names more reused throughout Transformers mythology.

* 1984 his original toy form so bad@$$ it is now an illegal toy in the U.S. as an exact replica of a real firearm, the Walter P-38 pistol.  Since he was reformatted into Galvatron by Unicron, he made few other appearances in the G1 series.
* 1987 as a decoy.
* 1990 in Action Master form
* 1993 G2 green and purlple tank, surprisingly, it was his first vehicle form!.
* 1994 G2 air power rocket launcher
* 1995  a very uncool "gobots" version.
* 1996 Beast Wars Alligator and the more well known purple T-rex.
* 1997 in Machine Wars form!
* 1998 in Transmetal form (my personal favorite!)
* 1999 as a Transmetal 2. 
* 2000 in Beast Machines.
* 2001 as 6-changer RID Megatron
* 2002 as Armada Megatron and Megabolt Megatron, (a Beast Machines version toy in R.I.D. packaging! Go figure!
* 2004's Energon Megatron. In this year he was also released as a toy gun accessory for Masterpiece Optimus Prime!
* 2005 a very popular Cybertron Megatron (Leader Class) and Legends Class.
* 2006 his first reappearnce as a gun in 22 years: Classics Megatron.  Plus several titanium versions, Beast Wars 3", Cybertron 3", GIJoe comics version of Megatron 6"
* 2007 many toy forms relating to the Movie: Legends Class, G1 Real Heroes, Movie Real Heroes, Fusion Blast (FAB) Megatron, Robot Replicas, Robot Heroes vs. Pack, Voyager Megatron (frozen), Voyager Megatron (metallic) Megatron Unleashed, the definitive Megatron toy of the year Leader Class.  Then Titanium 3" movie, 6" War Within Megatron.
* 2008 Voyager Megatron Cybertron Mode, 2-pack Deluxe, Leader Class Animated Megatron...

...undoubtedly, there will be many more to come!