Ronald Greer is a Master Sergeant in the United States Marine Corps, who was assigned to Icarus Base. He is a member of the team sent and later trapped aboard the Imperial vessel Destiny. Greer has difficulty trusting people who are not part of the military, such as Dr. Nicholas Rush. Surprisingly, the only civilian that Greer appears to trust to any degree is Eli Wallace. At first glance it seems he has anger issues, but he cares about those aboard the ship. Although he is clever and calm during a struggle, he believes that he can only count on other soldiers during combat and has a hard time trusting the non-military personnel. His sense of humor is unusual but good at mediating conflicts when they arise.