Born in 729.M41, Carus grew up on the Frontier World of Ysai Ydumee in the Golgenna Reach of the Calixis Sector. Carus experienced a rough childhood, with his mother dying in childbirth to his younger brother Harren, and his father Johnan killed in the line of Arbite duty when Carus was a young age. Carus and Harren quickly learnt to rely on each other in order to survive, moving from city to city and avoiding attention.
 
During an attack by an underhiver scum, Carus protected his brother from attack, but in the process lost the fine motor function of his right hand as it caught the scum's blade. Although able to escape with their lives, the two remained vulnerable and without a proper upbringing. The brothers were shortly inducted into the Schola Progenum, where Carus had to learn to use his left hand after losing the natural use of his right. Despite the initial challenge, Carus became surprisingly adept with his left hand, developing a proficiency for one-handed weapons such as pistols, being one of the highest ranking in shooting drills among his fellow Progenum. Carus was chosen as particularly gifted in combat despite his drawback, and joined the ranks of the Adeptus Arbites following in the footsteps of his father.
 
Shadowed by the unexpected talent of his older brother, Harren progressively become abnegated from his Arbite duties and entangled himself in Xenos technology, unable to resist the Heretical temptations for power. As Carus rose the ranks of the Adeptus Arbites after he reached adulthood, he learnt of his brother's secret and was torn between his oath to the Emperor and the only family he has truly known. Harren was branded a Traitor, now dedicated to the Dark Gods, and escaped across the Golgenna Reach, in the process abandoning his newborn daughter. In pursuit of his brother, Carus adopted his voidborn niece as his own, naming her Ryna. Losing the trail of his brother, Carus continued his work on capturing and maintaining a hold on the Xenos tech trade within the sub-sector. Carus gained the attention of the Ordo Hereticus and Ordo Xenos of the Inquisition, and soon realized his adopted daughter possessed psychic powers and great potential. Carus was forced to surrender Ryna to the Black Ships, and through embittered contention, was able to broker a deal with Inquisitor Wroth that Carus would work as long as Ryna would not be left to suffer the same fate as her father. Wroth agreed and immediately put Carus and his skills to use. With the fate of Ryna placed in the Inquisition's hands, Carus could continue the search for his brother while also investigating various cases on behalf of the Ordo Hereticus.