The Fallen is:
1.A guy who dosen't Die
2.A guy who has given up.
Megatronus Prime is one of the original 13 transformers created by Primus. He betrayed them, and joined Unicron. He killed Vector Prime. Because of this, he became The Fallen. Later, Prima banished him and Unicron in a black Hole.
The Fallen returned years later with a sidekick, Scround. When The Ark landed on Planet X, he tried to kill them. He killed Optimus Prime, and Landmine. later, Scround became Zeta Prime, And Hot Rod got the matrix. realizing no matter how many Primes he killed, there will always be another one, he gave up all hope, and banished Himself in a black hole.