Short answers, pulled from the story.
King Claudius of Denmark is the antagonist in the play written around the year 1600 by William Shakespeare. He actively opposes his nephew Hamlet by murdering his own brother to seize the throne and marrying the widowed queen. This character serves as the archetype of the literary antagonist whose primary function is to actively oppose the protagonist and their world order.
The detective L serves as the antagonist in the manga series Death Note while Light Yagami acts as the protagonist. Light Yagami is a high school student who gains the power to kill anyone whose name is written in a supernatural notebook and becomes the central figure driving the plot. L pursues Light relentlessly yet represents justice and moral order in this narrative inversion.
Macduff emerges as the antagonist to the protagonist Macbeth in the play Macbeth. Macbeth is the character whose journey the audience follows even as he descends into madness and murder. Macduff opposes him representing the rightful order and the consequences of Macbeth's actions.
Inspector Javert is the antagonist in Victor Hugo's Les Misérables who pursues Jean Valjean the protagonist. Javert embodies the rigid and inflexible application of the law and creates moral and ethical dilemmas for the audience. His dedication to duty leads him to destroy the life of a man who has reformed and done good works.
Almost every character other than the protagonist Holden Caulfield may be considered an antagonist in J.D. Salinger's The Catcher in the Rye. These characters represent the phoniness and hypocrisy of the adult world that Holden despises. The antagonist can also be a force of nature or a societal norm that creates conflict against the environment itself.
J.R. Ewing played by Larry Hagman and Alexis Colby played by Joan Collins are the antagonists in the television series Dallas and Dynasty. These characters were designed to be the main enemies of the protagonists yet their charisma and complexity made them the most memorable figures in their respective series. Their roles as antagonists allowed the writers to create high-stakes conflicts that kept audiences coming back week after week.