DJ is the hidden supporting antagonist in Star Wars: The Last Jedi. He is a spy working for General Hux and The First Order.
History
DJ meets Finn and Rose inside a prison belonging to The First Order. Pretending to be a prisoner for The First Order, DJ offers Finn and Rose to escape with him, so he can sneak them into Snoke's throne room. He brought them to The First Order's mothership, and informed Phasma about their locations. Phasma eventually reached Finn and Rose, and took the two to Hux. DJ is revealed to be an agent working for Hux, and that he plotted to sell them out and get the two executed. What happens to DJ next is unknown.