Who is John O’Neill? Why is he relevant to the narrative of the book?

As the FBI agent in charge of counterterrorism, John O’Neill is Osama bin Laden’s primary adversary in The Looming Tower by Lawrence Wright. He is vital to the narrative because he creates a conflict for the terrorists. However, John O’Neill's worthiness as an adversary becomes debatable when his flaws are revealed. We find out that he is a philanderer with a bad temper and large amounts of debt. He is then forced to retire from the FBI after leaving a briefcase containing confidential documents in a public place. It is the ultimate irony when John O’Neill becomes the head of security at the Word Trade Center and dies in the 9/11 bombings. So, he not only loses his life, but he also loses in his conflict with Osama bin Laden.