Dune was part of the original group of men that Ladd Russo assembled for the kidnapping aboard the 'Flying Pussyfoot'. To get aboard he killed the about-to-retire conductor 'Tony' and stole his conductor uniform and subsequently wore it.

Spoiler

Later Claire Stanfield reveals to Dune whilst interrogating him that Tony was the man who taught him everything about conducting a train and is enraged. Dune is then killed by Claire who pushes his entire right arm into the train tracks, then his face.