M'Gubgub is an immense entity from the reality Marvel Universe. It so large that his mass is stretched across nine million light years. M'Gubgub's name is known throughout the universe, and his arrival is met with fear and mass evacuations of the populace of the worlds he approaches.
When Alfie O'Meagon was attempting to spread "help" to the universe, he came across the world that was home to the Borborgym. The people of this world scoffed at the idea of him helping, as they'd been visited by others who had come to help, and ultimately caused nothing but trouble. Among the many problems these saviors had left behind was a device that the Borborgym called the "Arrrgh" that gave immediate omniscience to anyone who touched it (they would then leap to their deaths, screaming "Arrrgh"). As Alfie O'Meagan was shown this device, a member of the Borborgym decided to touch it, saying he had spent thousands of years trying to discover the meaning of life and was sick of doing it the hard way. Touching the ball, he said the word "M'Gubgub." This immediately led to the evacuation of the planet, much to the confusion of Alfie.
As Alfie waited on the planet for the arrival of M'Gubgub, an immense entity arrived, an entity many times the size of the planet itself. Alfie attempted to increase his own mass to meet this newcomer's, but was incapable of making it even halfway. This new entity then told Alfie that there were things he couldn't even begin to imagine, and when Alfie addressed him as M'Gubgub, the immense entity repeated the name, then fled in fright. A giant hand then appeared behind Alfie, larger than the entire being who had just fled.
Alfie attempted to befriend this entity, but M'Gubgub instead of learned of Alfie's past, including his ability to warp time. Feeling this was a threat to the universe as a whole, he informed Alfie that he had to destroy the Earth. Alfie then attempted to lead him away from the Earth, but realizing there was no hope of that, he went back to the planet Earth.
Arriving on Earth, Alfie informed his old friend John Doe that he was the only one who could defeat M'Gubgub, and then imbued John with part of his essence, greatly amplifying John's pre-existing powers. John's mass involuntarily increased, but he was still only half the size of the essence that M'Gubgub was leaving on the earth. After a brief physical confrontation, John released his original power, only greatly magnified, and reversed time within M'Gubgub, causing him to pull back within himself, and freeing Earth from his danger.