What does the tort of defamation protect, What does a plaintiff need to prove to win

What does the tort of defamation protect? What does a plaintiff need to prove to win a case for defamation? What is the best way for a defendant to win a case for defamation? In other words, what is the best defense? Do some research online and find a famous defamation case. It can be against a business, about a public official... You choose. Summarize the case for your group and report on who won, as well as your comments about the case.