The feared antagonist in the story of "Harry Potter" is Lord Voldemort, also known as Tom Riddle. He is a dark wizard who seeks to gain power and immortality, primarily through the use of Horcruxes, which hold pieces of his soul. Voldemort embodies fear and tyranny in the wizarding world and is the primary source of conflict throughout the series. His desire for control and belief in blood purity leads to violence and discrimination against Muggle-born wizards. Harry Potter, the protagonist, stands as his main adversary, epitomizing the fight against prejudice and the value of love and friendship.