Attached to the 108th Infantry Battalion, Sergeant Daniels led Elliott Tercorien's squad in an battle pitting the U.S. Army against the Chinese. Part of a medical team, Daniels erected field tents and radioed for evacuations after surgery, or if a casualty's wounds were too severe to treat on the battlefield.
Among the Stars: He can be revived from his stasis pod along with Private Beckett, either without Elliott preparing their memories (in which case, Daniels is hostile), or after their memories return (in which case, Daniels fights alongside you until falling during the assault on the Cryo Storage facility).
Given that he is the one that holds the highest rank out of any others in Elliott's squad, it is probable that he, not Elliott (who is a private), was the squad leader.
Both he and Beckett lose health naturally over time and will not heal themselves, even if somehow given stimpaks; this will eventually lead to their deaths. Additionally, Beckett and Daniels will die immediately upon destruction of the cryo lab generator as part of a scripted event.
If Daniels and Beckett are revived while Pek is with the player, they may attack and eventually kill Pek, while being friendly to each other, Elliott, and the player.