During the Tarsian War during the mid-24th century, Danar volunteered for service in his planet's military. Like many other Angosian soldiers, he was subsequently subjected to intense physical and psychological conditioning and chemical manipulation. The effect of this was to cause his mental and physical abilities to become enhanced when danger was perceived. It also prevented his life signs from being detected through conventional means.
After the war, Danar and the other soldiers attempted to integrate back in to Angosian society. With no attempt to reverse their conditioning, the soldiers quickly became violent at the slightest provocation. A referendum over their future was held, and they were subsequently relocated to the penal settlement Lunar V where they were well fed and comfortable, but unable to leave.
In 2366, Danar attempted to escape from Lunar V, and killed three guards in doing so. The USS Enterprise-D was in orbit as the Angosians were petitioning for entry into the United Federation of Planets. Danar proved incredibly difficult to capture and demonstrated extreme cunning and tactical ability, confounding even the crew of the Enterprise-D. He was eventually outsmarted by Data, but when he was transported aboard it took Commander Riker, Lieutenant Worf, Chief O'Brien, and two security officers to restrain him.
While in custody, Deanna Troi discovered the truth about his imprisonment. As the Angosians attempted to take him back in to their custody he escaped once again, apparently doing the impossible feat of shattering a transporter beam, and then outsmarted the Enterprise-D's crew and captured the prison transport sent to recover him. He attacked the Lunar V prison and released a number of other prisoners. He subsequently stormed the Angosian capital city and held Prime Minister Nayrok and a number of other officials prisoner. Captain Picard refused any further involvement and departed, leaving the Angosians to deal with the situation. (TNG: "The Hunted")