IndustryGamers, Bungie's Joseph Staten shared some insight on the studio's character choices for Halo's enigmatic Master Chief. According to Staten, it was a conscious design choice to keep players in the dark about specific details from the Chief's life. It helped immerse players in the role, said Staten, adding, "The less players knew about the Chief, we believed, the more they would feel like the Chief."
Staten shared a few other details, notably that Cortana began solely as a "functional design requirement," namely a guide for the player; however, as she evolved, said Staten, she grew to highlight the Chief's humanity. Check out the full article for more on Bungie's design choices, including how the team introduced themes of loneliness and abandonment in order to help players "feel the weight of the Chief's heavy responsibilities" throughout the series.