Lieutenant Cooper is a member of the Lewis and Clark crew. He was one of the three survivors found aboard the Event Horizon by the second search and rescue team. He is suggested to be very close to Justin.
Cooper escape certain death by blowing out his air tank to get back to the event horzion
Through out the movie
Cooper somewhat acts as the comedic relief for the movie, constantly cracking jokes, narrating his surroundings and even acting very casual and like a normal person throughout the movie. Cooper is extremely close with Justin, them making jokes with each other, deeply caring about Justin after he is injured and them being 2 of the 3 survivors. Make of that what you will.