Created by Primacron at the dawn of the Universe, Unicron is the ultimate Transformer. His brute strength and power are beyond comprehension. Besides being in planet mode, he can also transform into a menacing robot, capable of tearing apart planets with his bare hands. Among his loyal, and fearful, minions are the Quintessons and whoever else he happens to lure into making a pact with him. His only known weakness is the matrix of leadership.

Created by: Primacron

Reason: Primacon wanted Unicron to destroy worlds and leave the universe as a blank slate for his use.
Weakness: Matrix of Leadership
What he did: Created: Galvatron (from Megatron), Cyclonus (Bombshell {or Bombshell clone}), Scourge (Thundercracker), the Sweeps (Kickback ,Shrapnel, Skywarp, and a Cyclonus clone. These were made from the other Decepticons thrown out of astrotrain.

"Death":

1. In the Movie

• Cyclonus and his followers traveled to Unicron's dormant head to reactivate his central computer in the hopes of finding Galvatron. Cyclonus believes that Unicron is truly dead, but Scourge on the other hand does not. It turns out that Scourge was right and Unicron was alive, though rather impaired in his current state. Unicron later makes a pact with the ghost of Starscream: He will give Starscream a new body in exchange for a new set of eyes and a new body (Cybertron). Starscream obtains the eyes that he desires from Metroplex and Trypticon, but Unicron was unable to get Cyberton for a body.
  

The following passage is from the TF FAQ
written by Steve Stonebraker
srstoneb@cc.owu.edu
bc872@freenet.carleton.ca
http://www.owu.edu/~srstoneb

8. Did they ever make a Unicron toy
Not really. There was a prototype made, but it was never released anywhere. As you would expect, it was pretty large. Supposedly the photo in the Special Data Book mentioned below shows Rodimus Prime coming up to slightly below Unicron's knee. Anyway, here's a letter that was once printed in Action Figure Digest on the subject:

"Dear AFD,

• After reading Don Ferguson's letter in issue #12, I was surprised to find your information regarding the Transformers character Unicron was incorrect. A Japanese book, "Transformers the Movie: Special Data Book" (distributed by Takara) shows that there were two prototypes. The first was rather small, while the second was about the size of Fortress Maximus (about 21.5 inches). The larger one said ten phrases in Orson Welles' voice. According to my friend in Japan, the article says Hasbro USA did not like the first prototype, thus Takara produced the larger one (shown above). I'm guessing Hasbro rejected this one because it would cost too much to produce."