Original sentence: Given that deceit and obfuscation are Mephisto's stock in trade, anything he himself has presented regarding his origin can be untrue, but one theory proposed in the comics is that Mephisto (and many of the other "Hell Lords") was created from the primeval concentration of evil energy left in the wake of the fleeing Elder Gods when they were driven from the Earth by the entity Atum millions of years ago
Edited sentence: Given that deceit and obfuscation are Mephisto's stock in trade, it is doubtful that anything he himself has presented regarding his origin is true, but the most plausible theory  is that Mephisto (and many of the other "Hell Lords") was created from the primeval concentration of evil energy left in the wake of the fleeing Elder Gods when they were driven from the Earth by the entity Atum millions of years ago