This story arc is details the birth and life of one of Marvel's most prominent super-entities, Galactus! The story is actually about the trial of Reed Richards of the Fantastic Four among the sentient races of the known universe. Through the testimonies of survivors of many worlds ravaged by Galactus we learn of Galactus' history. We also learn of the universe that existed prior, and his necessity within the ecology of the universe.
Reed Richards is on trial because he "saved" Galactus from perishing...which led to the consumption of several planets throughout the universe. The executors of the trial are holding Reed Richards responsible for the trillions upon trillions of life lost.