The primary antagonist in Katherine Anne Porter’s novella Pale Horse, Pale Rider is not a living thing, but in no way can it be categorized as static.  Porter’s autobiographical story is about her experience surviving the influenza pandemic that swept the globe in 1918, leaving as many as 50 million people dead.  Around 675,000 Americans were among those dead, 43,000 of those were soldiers, a fact central to Porter’s history and to her story.  The antagonist in Pale Horse, Pale Rider is the influenza.  Influenza is a virus, not a bacteria and, as such, is not categorized as a “living” thing.  While not technically categorized as “living,” however, viruses like influenza might just as well be given the manner in which they spread among hosts and invade living cells.  Because of the actions that occur once a cell is invaded by a virus, it cannot be considered “static,” but, rather, “dynamic.”  Any literature professor posing this question, it is hoped, understands the distinctions between bacteria and viruses, with the former most definitely constituting living beings. 

Beyond the role played in Porter’s story of the influenza pandemic, another antagonist could be Germany, America’s enemy in the Great War (in addition to the Ottoman Empire, but that was more a British game than anything).  Fears bordering on paranoia regarding a nation’s enemies commonly result in the proliferation of conspiracy theories that generally have little or no basis in fact.  In the case of the coincidence of the war and the influenza pandemic, the wide-scale toll taken by the latter across the United States fed such stories regarding Germany.  In Pale Horse, Pale Rider, Porter depicts two of Miranda’s colleagues discussing such theories:

“’They say,’ said Towney, ‘that it is really caused by germs brought by a German ship to Boston, a camouflaged ship, naturally, it didn’t come under its own colors.  Isn’t that ridiculous?”

To reiterate, then, the main antagonist is the virus devastating mankind.  A secondary antagonist would be Germany, the adversary in the war raging in Europe.