Very little is known about the possibly mutant binary husband and wife team that is Mr. and Ms. Black.
It's believed that both of them share the ability to link each other's neural frequencies to communicate telepathically and/or psychically with the rumor that they could even communicate great distances to include between the Earth and the Moon.
Both are highly skilled in melee and ranged weapons, combat techniques and know how to operate and utilize every weapon known to mankind. When the two fight together, they are a deadly threat in that they work in unison in combat, complementing each other's actions, moves and tactics.
The previous G.U.A.R.D. Director, Hart, set both Mr. & Mrs. Black as the leads in XGUARD, with both working with global (and extra-global) resources with their 'exactly' 222 XGUARD personnel. XGUARD has discovered thousands of threats, malicious plans and even set procedures to stop, detail and at times, even kill those identified as 'too dangerous to live'. Together, XGUARD also performs Black Ops missions, monitoring or GUARD personnel, and in conjunction with PSIGUARD, ensure that no GUARD personnel compromise GUARD's internal security or operations. They are also used as an internal affairs service should criminal or personnel investigations require an experiences hand in assessing and deciphering situations or malicious activities in GUARD. In the event that XGUARD believes there is a compromise of GUARD, Mr. & Mrs. Black (and only those two) are allowed to buck the chain of command and go directly to the Executive Division to discuss/identify the concern.
Mr. & Mrs. Black are rarely seen anywhere within GUARD's HQ, however, with the expectation that both are also masters of disguise, they can easily blend in anywhere they go.
The question most commonly asked about Mr. & Mrs. Black is simply, "Can they be trusted?"