Background and early life
As a young man, Winston would skip school and meet his friends at the mall to watch films and eat fast food. He was fairly interested in a young woman named Roberta Coen. Winston also seemed to have an interest in hunting, as he is seen in an old photo of him holding a hunting rifle.
Events of American Dreams
In the aftermath of the Cordyceps brain infection pandemic, he joined the United States military and was stationed in the Boston quarantine zone within a mall in a small camp with a horse. As one of the soldiers patrolling the area, he eventually encountered Riley Abel, a fifteen-year-old girl who lived in the school. The two became friends, Winston humoring her friends whenever she would bring them around to visit and Riley providing him whiskey in exchange for certain things and privileges while in his company.
He presumably allowed Riley’s friends to ride his horse, Princess, but would cut their time short because he was too lazy to take them around the entire mall. Winston's interaction with Riley, however, suggests that he is often in trouble with his superiors because of her rebellious nature.
When he meets Ellie, Riley asks him to teach her how to ride a horse in exchange for bringing him another whiskey. Winston agrees and takes Ellie for a ride around the mall on Princess. The time he spends alone with her allows him to reminisce about the mall and his life before the infection. When he and Ellie return, he tells Riley that she should head back to the school as an explosion erupts outside the mall. In haste, he mounts his horse and heads off to find his unit.
Around summer of 2033, Winston wrote a letter of complaint to his superior, Major Banks, requesting more manpower to handle the growing issue of refugees (some of which were infected) flooding into the mall from the Hartford quarantine zone, which was falling apart. He personally had to kill three runners and was frustrated Banks would likely ignore his warning. At one point, after coming back early from a patrol, Winston spotted a crying Ellie at his camp but did not comfort her and instead slipped away.
Events of The Last of Us: Left Behind
Sometime after his encounter with Riley and Ellie, Winston eventually died of a heart attack while out riding Princess. He is one of the few known survivors of the outbreak to die of natural causes. His camp is later found in the mall by a wandering Riley and Ellie. They remark how much younger he looked in a photograph and Ellie (player-determined) and Riley share a drink to honor him.