Mac is willing to endanger his own life to protect his colleagues, and has done so on several occasions; offering to trade places (as a hostage) with not only his teammates, but civilians as well.
Mac is single-minded when it comes to catching the bad guy.
Mac is also very intent on the integrity of the lab. He fired Aiden Burn for even considering planting evidence, even though she never did.
Mac holds all military personnel in high esteem, considering the uniform itself a badge of honor. He often dressed in fatigues as a child, indicating his interest in serving his country at a very early age.
Mac was originally from Chicago. He joined the Marine Corps, and was a veteran of the Beirut Bombings (where he was severely injured and has a scar quite close to his heart) and the the first Gulf War. After serving in the Marines, he was successfully discharged in March of 1992, having achieved the rank of Major. Mac moved to New York after his discharge. His father was a WWII veteran who took part in the liberation of Auschwitz in 1945. He died of cancer while Mac was still in the Corps.
Mac was a part of the military for many years, and still has proficient skills in fighting. He especially excels in unarmed combat, making it easy for him to take down suspects on the go.
From his service, Mac has gained an intimate knowledge of a wide range of weapons, and is proficient in many of them.
Mac is a skilled bass guitar player, and has a standing appointment on Wednesdays to perform with a jazz group.