Birth Of Entropy
Entropy was created at the beginning of time, possibly when Eternity was formed, Entropy came into being with the seven friendless.
Just as all the other friendless have purposes of their own, Entropy's purpose is to destroy, juxtaposed to his father, Eternity, whose purpose entails creation.
Entropy and Captain Marvel
Entropy engineered the insanity of Captain Marvel in Captain Marvel VI #1, causing him to see that, by failing to save the life of an unnamed alien female during a Badoon raid on their homeworld, he had let the Universe's greatest peacemaker die. ick, telling him that Captain Marvel's fate was sealed. When Rick asked him who he was, he merely replied, "I am no-one"
Later on, Rick woke up in a room without any knowledge of how he got there, and could hear the voice of Epiphany, Entropy's sister, conversing with Entropy himself. Rick then went to confront Entropy, at the time not knowing who he was. At the same time, Captain Marvel tried to kill himself, sending Rick into unconsciousness due to their symbiotic relationship.
Entropy later met Captain Marvel himself, entailing that it was he who drove him insane, but did not explain why yet. He then showed Marvel a variety of scenarios, one in which a man tried to please his father. Entropy then went on to reveal his true purpose and nature: that he was the offspring of Eternity, and that he was out to destroy the universe and wanted Marvel's help. That was why he drove him insane. Marvel gladly accepted.
Marvel and Entropy, along with Rick and Epiphany, stood in nothingness, the absence of Eternity. However, in his insanity, Marvel had developed a God complex, and this sparked off an argument between himself and Rick. To prove his point, Entropy asked Marvel whether or not he was God, but Entropy could not answer, because he had accomplished his purpose, and asked what was to come next. Rick suggested to do what he knew, and that was his father's purpose, to create. Creating something was the first new concept Entropy ever had and decided to do it. However, he had never thought of creating and didn't know how. Rick told him just to go with what he knew. All he knew was what his father was, so he created a big bang, recreating the universe, and became the new Eternity. Time rolled back on itself, until it came back to the modern day, and everything became as it was.
Powers and Abilities
Entropy had incredible godlike powers superior to that of most cosmic beings and on par with such beings as Eternity. His power allowed him to do virtually anything and everything. In his own words, he was "beyond the cosmos, outside its perimeters and parameters."