Galvatron is the reincarnated form of
Megatron.
Megatron fought to the
death with
Optimus Prime in
Transformers the Movie. When the
Decepticons were retreating in their shuttle (
Astrotrain the triple-changer),
Starscream--the second in command of the
Decepticons, jettisons Megatron into
space. It is then that
Unicron, the mechanical
planet that turns into a giant
robot, finds Megatron and rebuilds him as Galvatron.
Galvatron is like his former self in many ways. He still has a giant arm
cannon that can shoot mega-laser blasts. But Galvatron transforms into a giant laser cannon, instead of a hand gun like Megatron.
And Galvatron still has all the
millitary strategy, ruthlessness, and cunning of Megatron. However, Galvatron is somewhat psychotic, and his tendency to act on his emotions rather than logic has caused many Decepticons defeats to be worse than need be (after all, Megatron knew when to back off).
Oh yeah, Gavatron is also the name of the
Predacon leader in the
Beast Wars cartoon. But he's nowhere nearly as cool as the real Galatron.