From Tekken Zaibatsu Wiki
Craig Marduk fought against King during The King of Iron Fist Tournament 5. Although he lost, he and King had a friendly handshake after the match. Upon returning to his room, the lights suddenly went out and Marduk was attacked. When the lights came back on, he saw the suspected culprit, Armor King, whom Marduk thought he had finished off.
Thereafter, the world became engulfed in war. At the peak of the global chaos, The King of Iron Fist Tournament 6 was announced. Marduk reasoned that if he entered the tournament, perhaps his attacker would appear. Along with his new ally, King, Marduk entered the contest to find his attacker.