Kieran is described by Arthur as a "gentle buffoon". Duffy is soft-spoken and nervous, often stuttering when he speaks. He becomes genuinely frustrated whenever someone refers to him as an "O'Driscoll", and zealously told Dutch upon meeting him that he hates Colm O'Driscoll. Although the gang kidnapped him, he seems intent on earning their trust and becoming a fully-fledged member.  He generally has a kind-hearted demeanor and avoids conflict when he can, refusing to cause or continue conflicts.