As a child Cain was odd, he was born in Chernarus and spent very little time there, he always wrote plans on his journal about how he could kill different people he had met. When this was discovered, Cain was moved to the United States of America at he age of 10 for professional psychological treatment that was not available in his country of birth and was given help in the form of therapy which would set him be on the right path as long as he followed certain instructions; Be disciplined, be kind, and dont harm another. He was able to follow these rules by having a guide, someone who was pure and truly good. That person was his friend "Sofia".
Cain had known Sofia for a long time now, one could have considered her his best friend and eventually Cain fell in love with her. As the years passed both he and Sofia moved back to Chernaurus when Cain had just turned 17 so he could meet his family after a long time overseas, the apocalypse came and both Cain and Sofia fled to a shelter nearby where they spent a couple of months, eventually Sofia died of disease, Cain no longer had an example to follow and blinded by anger he killed everyone in the shelter he and Sofia once resided.
2 years passed and Cain was wondering the wastelands of South Zagoria when he got a strange message from his transmitter: "Long time no see brother". Cain and his long lost brother had been reunited, Coco knew all about Cain and the shelter he destroyed as he had been looking for him shortly after the outbreak and out of fear Cain would hurt anyone he cared about, Coco met with him, captured him and imprisoned him on the outskirts of Chernarus near "Stary Yar". Coco checked in on him every day at around 6:00 PM through his radio, but one day Coco stopped. Cain finally had a chance to escape.
He set out to look for his brother so he could have his revenge, after a couple of days searching, Cain met with a man who claimed to know what happened to his brother and his name was CJ who eventually became his guide, teaching him about the terrible things that he had done to other people in Chernarus and Cain followed his example for some time, he killed and he robbed people for pleasure until he met a mysterious woman. This woman helped Cain out of the endless cycle of death and pain he was in, they now roam Chernarus looking for purpose.
3 months passed and the mysterious woman joined a group, leaving Cain alone to roam Chernarus. But, one day Cain met with the woman where he revealed his love for her and starting a relationship her, after some complications the woman had to leave him and as a test of loyalty and commitment towards the group she had joined she had to kill him. The group caught Cain and was shot with a shotgun at close range. They left him for dead on the street.