Clark was a former Russian spy and a soldier of H.A.R.M.
Cate first meet Clark and his wife Martha in Grand Caravan Hotel, Marrakech, Morocco. From the letters Cate found in their hotel room,she discovered that Clark is a Russian spy and is going to leave Martha and go back to his first wife.
A few months later he defected from Soviet Union and join the terrorist organisation H.A.R.M. Clark was station in a secret underwater H.A.R.M. base in Aegean sea, wich Cate inflitrated to save Magnus Armstrong. Clark was trying to kill Cate, but was unsuccessful and Cate kill him. After she search his body, she found a letter adress to Martha.