William McClane was a veteran of the Chernarus conflict, a NATO peacekeeper in the region. He had been pretty seriously injured, saw a close friend die by stepping on a mine that wasn't found, and witnessed a plethora of other horrible war time injuries. All of these things led to him being honorably discharged after failing a psychological screening, so he went back home to Paisley, Scotland, a small peaceful town. After a few years of therapy he decided to go back to Chernarus to confront those demons remaining in his subconscious... but little did he know what he would be confronting.
When he reached Chernarus in early July 2017, it seemed like it was peaceful and calm, and with hope he stepped out into the streets of Красностав (Krasnostav). But then, the unthinkable happened. The first wave of infected hit only a 3 days after his trip had begun, his first sighting of the infected was at a hospital where he was visiting a friend. He saw a man, he later found out was infected, missing an arm being restrained by doctors and nurses, seemingly unfazed by his missing arm and in a manic state trying to attack whoever he could reach with his good arm. He was like a rabid dog, trying to grab anyone and finally he got a hold of a nurse and bit her. Seeing the chaotic scene William started having his first signs of PTSD in months. William quickly left the hospital and went back to his hotel room to help himself calm down, and he thought about the scene and why it might have been happening. He watched the news to try and see if there was any coverage on this crazy man at the hospital and found out it was happening all over Chernarus. William knew... the beef. That damn beef infected the majority of Chernarus. Chick-fil-a was right.. eat more chicken.
During the initial days when it was officially labelled an outbreak, William mentally broke and started killing all the cows he came across to try and stop the infection from spreading to the rest of the world. He had the idea to try and find other NATO veterans that might be in the country to try and get payback for what happened to squad members back in '09. He hasn't found anyone he trusts yet, but he is hoping to find some allies in the infected wasteland. He remembered a man he met back in his peacekeeper days named Ryan Dudley that he was going to try and ask around for since Ryan was one of the people William knew he could trust with his life. William has been wandering and scavenging since the society fell, surviving and avoiding killing other survivors wherever possible in hopes of the infection dying off and building a new safer society.