AOne common question that fans often have about the movie is why Ultra Magnus, who has been blown into pieces, could easily be repaired whereas Optimus Prime dies after his midsection is injured. We see during the fight between Optimus and Megatron that Prime receives many hits in the same area, as Megatron batters, cuts and blasts him with a gun. Prime's body simply sustained too much damage to be repaired.Meanwhile Magnus explodes into many small, but otherwise intact parts, allowing the Junkions to repair him easily. This scene was better explained in the movie's original script, where instead of exploding, Magnus is merely pulled apart. The scene had to be redone after it's been deemed too violent, but since Magnus's rebuilding remained an important part of the story (his toy had to be promoted, after all), he had to survive somehow, and as such, the explosion doesn't damage his parts, only separates them.
AUnicron's origin is revealed in the Season 3 episode of Transformers, Transformers: Call of the Primitives (#3.26). He was created by a strange gnome-like ancient entity called Primacron, at the dawn of the galaxy. Unicron later rebelled against him and left his creator behind.This origin story is notable for being ignored by each end every subsequent Transformers media. Unicron's "true" origin is related in the Marvel Generation 1 comic series, which depict him as an ancient god of evil and destruction who's capable of traveling across dimensions and thus different Transformers series.