There's not much history about Casque, but there are some we learned from him. Casque raises Kiani, a female Elite Blue and took her as a student and trained her to become a warrior. After getting captured by Admiral Maylander, Kiani manages to save Casque and the captives from Maylander's force. Casque later reveals to Kiani that he is the member of the Black and he left her, felted crushed and upset.
Casque, now with his brethren met Aspen Matthews, telling about her and the history of the Black. Casque introduces Aspen to her father, Rahger and learns more about her origins.