I love antagonist background day!

I think a sympathetic antagonist changes a good book to a stellar one. The antagonist's motivations need to be as clear cut and understandable as the protagonists, if not more so. You can't create a bad guy just to fill a spot. A truly fantastic antagonist isn't against the protagonist just to be against them, their motivations are just opposite. Or, in some cases, they're motivations are the same, they just have a vastly different idea as to the best way to accomplish things.

I love delving into my antagonist's background and writing from their POV and getting a better understanding of why they make the decisions they make later in the book.

"Every villain is the hero of his own story." (And if my story had been written 1000 years before the events of the novel, he would have been the hero, easily).

My poor conflicted antagonist. They broke him and now all he wants is to be freed and reunited with the love of his life. Unfortunately, it comes at a cost my protagonist is just not willing to pay. Remember, everyone's the villain in someone else's story, and this time it's your protagonist's turn!