Heaven and Hell were (wil be) a pair of future heros from the Promethian Age, around the 700th century, In this time they were members of the Pancosmic Justice Jihad, which had a very hostile attitude to other worlds and had a harsh way to execute justice, including preemptive attack on worlds considered potential threats.
Because the aftermath of the attack of Imperiex on earth, and the subsequent actions of Superman it is unclear if Heaven and Hell would ever exist at all in the future.