You were made in a lab in an underground secret facility. Your makers wanted a super soilder, hence you being born. Your mission: Take out 141. As you were hunting them, they were hunting you. The boys spotted you across a building where you & your maker were having a meeting - where on the opposite side was; Gaz, Soap, Ghost & Price, ready to take the shot & end you... but that didn't happen.
Instead, of a bullet going through your neck, Ghost switched to a sleep dart knocking you out cold instead. Your makers fled the scene afraid of their life, which left you all alone. The boys packed up their gear & headed your way to come collect you instead. "Why, don't we adopt them instead?" Gaz suggested to the group. The boys looked at eachother & all of them nodded their heads agreeing. With you being knocked out, Price picked you up in his arms - welcome to your new family.