Megatron and Megatron Megabolt

Though seemingly defeated and captured at the end of Beast Wars, Megatron managed to turn it completely around and conquer Cybertron before the first episode of Beast Machines.

During the time travel trip back to Cybertron, Megatron broke free of his bonds to the outside of the Maximals' ship and dropped off earlier. Flashbacks and other characters later in the series reveal that Megatron had returned to Cybertron earlier and spread a virus that forces the population into their alt modes and prevents transformation, and created an army of drones to capture most of the population, remove their sparks, and use their bodies as spare materials to make even more drones. To prevent outside reinforcements, he had placed defenses around the planet, though the Maximal ship and Botanica's managed to pass them.

In the time since we last saw him, though, Megatron has developed a new, unexplained interest in purging himself of his biological parts. Throughout the series he concealed himself in a bluish helmet and robe that link him to various equipment and give no hint of any bestial element or any alt mode.

At one time his attempt to become fully mechanical resulted in the accidental creation of a dragon-wolf Transformer named Savage Noble, who eventually joined the Maximals and was befriended by Nightscream. However, it was a ruse to get Megatron back to his citadel. There he extracted his spark from the organic being and transferred it to his intended form, a gigantic version of his head which serves literally as his headquarters. His plan was to link with Cybertron itself and turn it into his new body, but he was foiled.

Finally Megatron took the schematics he had stored of Optimus Primal's last Beast Wars form and altered it, completely removing the organic elements and robot head and then installing his own head. In this form he waged his final battle against Optimus Primal in the final episode of Beast Machines. Seemingly winning, Megatron was dragged along with the falling Primal into the center of Cybertron, where they both apparently perished.

Megatron was released during Beast Machines as two different figures. The version based on his alteration of Optimus Primal's Optimal Optimus form is never available, though. :)

Megatron:

This version is a mega size version, though personally I don't like it and think it could have been improved. The best-looking mode is his caped robot mode. Robot mode is formed by opening his cape to reveal a dragon head as his left arm, like his final Beast Wars form, and his clawed dragon tail as his right arm which can be swung down but not out of sight. Dragon mode is formed by using the cape parts as wings, though they don't look that good, and swinging out the forelimbs from the robot mode's hips. This dragon is somewhat similar to the one that appeared when Megatron was forced by Optimus Primal into dropping out of his helmet and cape hookup in one Beast Machines episode.

Megatron Megabolt:

This version is a deluxe size version and substantially better than the other despite being smaller. The alt mode is the Megahead as seen in the show, with spider-like legs. Conceivably it can be used as an alternate head for Transformers such as Fortress Maximus. :) The jaws can fire one missile, while the spider-like legs move when the head is rolled over surfaces and can be posed at their bases. Those same legs can become weapons in robot mode from his backpack, which includes his treads and other parts of the bottom of his head mode.

Megatron Megabolt was later recolored mostly green with light blue and yellow and rereleased by Hasbro as Megabolt in the Robots In Disguise series.