I have an idea of a Terran who is in their mid-50s. They are generally quite unassuming, light-hearted, and use humor a lot in response to tense situations. I was considering having their name be Colter "Colt" Dutton. 

He participated in the Umbral War for many years on the Crux Tenebrous side and held the rank of Colonel (or lore equivalent). Colt was a loyal, dedicated soldier who believed in the Crux's cause. However, on his last mission, he was ordered to commit an atrocity of genocidal proportions. Since then he was given the moniker "Nightmare of Votian" (Votian is just a word I came up with for a group of people). After that moment, he deserted his post and became a space outlaw.