Kung Lao trained with the Shaolin Monks to become one of Earthrealm's most skilled defenders. But his immaturity and impetuousness prevented him from being taken as seriously as his friend Liu Kang. Despite Lao's shortcomings, he was able to defeat both Shang Tsung and Quan Chi in Mortal Kombat. But his life was cut short when Shao Kahn brutally murdered him. In death, Kung Lao's soul was collected by Quan Chi, who used it to create and evil "revenant" version of Kung Lao. He now serves Quan Chi and the Netherrealm.
After Shinnok's defeat, Kung Lao found himself trapped in the Netherrealm, his soul corrupted by Quan Chi's dark magic.
There he would have remained but for the aid of his cousin Kung Jin.
Together their Shaolin strength repelled the evil sufficiently enough for Kung Lao to escape that dark realm and control his inner demons.
Compromised but not lost, Kung Lao now exists as an agent of vengeance.
He will show evil no mercy.