Who is John Clark from Rainbow Six and what is their importance?

John Clark is a former CIA agent and Navy SEAL. He is in his late fifties when he is named the commander of the newly-formed covert anti-terrorism team named Rainbow, headquartered in Hereford, England. The British Secret Service is also based in Hereford. John Clark's code name is Rainbow Six. The organization is named Rainbow due to its multi-national team members. Upon moving his family to England, Clark's unit is immediately faced with outbreaks of terrorist activity in various European countries. Clark is a savvy and experienced leader and is up to the challenge. The biggest test of Clark's leadership is when he and his team must defeat a threat to all mankind.