Ronald Tracey

Ronald Tracey was a 23rd century Starfleet captain, who served as the commanding officer of the Constitution-class starship, USS Exeter during the late 2260s. Ron Tracey was described by fellow captain, James T. Kirk as being "one of the most experienced captains in the Starfleet." 
Despite his apparent experience, Captain Tracey violated the Prime Directive. Captain Tracey led an Exeter landing party to the surface of the planet Omega IV in 2268, where they inadvertently contracted the Omega IV virus and passed it along to the rest of their crew. Tracey remained on the surface while his crew died painfully in orbit, and found that the atmosphere provided him immunity to the virus. Driven to insanity by the loss of his crew and ship, and in violation of the Prime Directive, Tracey struck a bargain with members of the planet's Kohm faction and participated in their ongoing war against the Yangs. Newly armed with a few phasers, Tracey and his Kohm allies slaughtered thousands of Yangs. 
The USS Enterprise eventually discovered Exeter and the dehydrated remains of its crew. The boarding party, led by Captain Kirk, was immediately exposed to the virus and beamed down to the relative safety of the planet's surface, where they discovered Tracey. After his crimes were exposed, Tracey shot and killed Kirk's security guard, Lieutenant Galloway, subdued the landing party, and demanded a supply of phasers from Enterprise. 
Tracey erroneously believed the Omega IV virus held the key to immortality. He considered it an opportunity more important than the Prime Directive, and if missed, "...a crime against all Humanity." After his failure to enlist Kirk in his cause, Tracey and the Enterprise officers were captured by the Yangs. Despite Tracey's efforts, Dr. McCoy's research found that the unusually long life spans of the natives were the result of generations of evolution in reaction to deadly bioweapons used in the past. As such, there was no isolatable serum to extract to replicate that hardiness in other beings. The immunity is simply a matter of being exposed (for even a rather short time) to biological agents in the planet's environment, where any surviving lifeforms have developed immunity to the bio-war agents by evolution. 
In a last-ditch effort to regain control of his fate in the face of this crushing reversal, Tracey played on the Yang's superstitions and tried to convince them that Kirk and his officers were evil, and must die. The Yangs matched Tracey and Kirk in combat to the death, to decide the truth of Tracey's wild claims. The intervention of an Enterprise rescue party permitted Kirk to spare Tracey's life and place the once-respected starship captain under arrest.