Michael Bishop and Alexei Rector are agents of the CIA.
Prior to their current employment both men had served with distinction in separate but equally challenging divisions of the U.S. military, each being part of that branch's most elite fighting force. Bishop had been a Force Recon Marine. Rector had been a Navy SEAL. Over the years they would become occasional ad hoc team members.
"Inter-branch operations were common, especially when it came to White House assignments and protecting dignitaries or other VIPs in times of crisis. In addition to their extensive combat and specialist training in anti-terrorist, hostage extraction, bomb disposal and intelligence gathering, some veterans from every branch were also schooled in the high art of dealing with non-military VIPs in emergency situations. Rector and Bishop were two such men, highly sought after by the State Department."
"Both men had been wounded in action and both had been awarded medals for their outstanding service. Navy Cross, Silver Star, Bronze Star, Distinguished Service Cross. Rector had suffered a concussion from an IED explosion in Iran. Nine years earlier Bishop had been in Afghanistan when his unit was ambushed by Taliban fighters. Two of his fellow Marines were killed, while Bishop had been shot in the lower abdomen just below his body armor. He was near death, but thanks to a skilled medic he survived to spend the next four months in hospital. After his recovery he was given an Honorable Discharge and was soon recruited by the National Security Agency."
When we meet them they have both been summoned to the Pentagon to meet with their sometime CO, a Navy Captain, who informs them that they have been given jobs of "ferrying scientists to the Pentagon" in an 'escort and protect' role. [Bit confusing that since in the case of Bishop, he was no longer in the military].
Jump ahead a fair number of years for the next recorded adventure and we learn that these two men were now agents with the CIA and had worked together on and off for nearly a decade.
In the sequel to the first adventure which appears to come next, Bishop is described as a Planetary Intelligence agent. I have not yet determined what Rector is.
In the fourth, they are both back as CIA operatives, this time referred to as 'senior' indicating both have been doing this sort of work for quite some time.