Flash (DCeased)

Flash is a supporting antagonist of the grim horror series known as DCeased, having succumbed to the virus that claimed many other heroes around the globe he would forever be changed from the benevolent "fastest man of Earth" into a murderous beat intent on wiping out the few survivors of Earth : he is also notable as the direct cause for Superman's infection and thus the one responsible for the final battle for Earth's future.

History
Flash was a hero for most of the events of DCeased, though he was forced into hiding by Batman out of fears of what would happen if he became infected - while this fear was justified the heroes had little choice but to enlist Flash regardless and despite considerable traumatic events and losses the group seemed to be on the road of saving what little was left of humanity.

Then in a cruel twist of fate an infected Martian Manhunter attacked the group, managing to infect Flash and triggering the nightmare scenario the now deceased Batman had feared all along.. Flash, now completely devoted to killing all remaining life on Earth, went on a Speed Force assisted rampage, murdering everything in his path at a rate of unthinkable carnage.

Superman knew that only he could stop Flash and save Earth from complete extinction, he did so by flying around the Earth to meet a rampaging Flash in the middle - flying straight through the undead speedster and shattering his former friend into pieces, killing him in order to ensure his threat was nullified.

Unfortunately for all involved there was not much time for mourning as Superman had become infected as a result of this confrontation - leading to the final events of the already long and brutal wars..

Trivia

 * DCeased is currently set in its own universe, completely separate from the mainstream DC multiverse.
 * the zombies in DCeased were not cannibalistic and were instead devoted solely to killing any life around them, this made them even more dangerous than traditional zombies and they also retained all the abilities of their host.
 * Flash was noted by Batman as a severe threat should he become infected, this prediction was proven true after he did become infected as only Superman was capable of stopping Flash from completely wiping out the human race in a matter of minutes.