Before his encounter with Dexter, during his killing spree, he is known as the Tamiami Slasher, due to the locations where his first crimes were found.
While as manipulative and fierce as his television counterpart, Brian is more controlled in regards of his urges. He likes to control others, either from the shadows or right in front of the person, using his fake smile and acting skills. Using his charm he is able to trick others into thinking he is not as dangerous as he truly is, the latest example of it being Rita Morgan in Dexter is Delicious.
He was able to bring Dexter near the doors of insanity during Darkly Dreaming Dexter, to the point where Dexter thought himself responsible of the deaths of all of Brian's victims. Thanks to his particular set of skills, he mirrored various of Dexter actions during his crimes, and his likeness with Dexter, made Dexter believe he was hallucinating most of his encounters with the Tamiami Slasher, who's face have not being seen by Dexter at the time. The only reason Dexter found he was not responsible for the deaths of innocent people is because Brian exposed himself to Dexter in the shipping yard and confessed the acts.
He does not value human life, at least not as equally as he values himself or the life of his biological brother, Dexter. Although he helped save Deborah and Kyle Chutsky from the cannibals in Dexter is Delicious, he only did it because of Dexter.
While Dexter's controls his Dark Passenger most of the time and usually summons it when needed, Brian fully embraces his, letting it take control most if not all the time. Known as Shadow Guy to Cody, Brian's Dark Passenger is similar in nature to that of Cody's, though in what way, it is never explained. Brian's Dark Passenger draws Astor and Cody in a way Dexter can't.
While having an usual ritual or standard procedure when killing his victims, just like Dexter, he is prone to change his methods and use whatever is at reach to accomplish his kills, his killing methods varying with the situation or scenario.
Unlike Dexter, he is not reluctant to use a firearm to kill. Brian used a shotgun to kill several cannibals in Dexter is Delicious.