Kevin Plunder is the eldest son of the British nobleman and scientist, Lord Robert Plunder. While searching for an undiscovered element he believed existed in nature, Lord Plunder discovered the hidden jungle on the Antarctic continent that became known as the Savage Land. There, he confirmed his theories by discovering the Anti-Metal (later determined to be an isotope of Vibranium), a substance that can destroy the molecular bonds of any known metal. Lord Plunder returned to his native England to find his wife had passed away in his absence. Realizing his own mortality, he locked away a sizable sample of the Anti-Metal he had brought back, and fashioned a small fragment of it into a medallion that could be used as a "key" to unleash its power. He then split the key in two, giving half to each of his two sons, Kevin and Parnival, as their inheritance.
When word of Lord Plunder's discovery leaked out, agents of an unscrupulous power tried to wrest from him the Anti-Metal's location. Saved from the agents by the arrival of his armed butler Willis, Lord Plunder decided to see to his sons' safety. While Parnival was sent into hiding with Willis, he and Kevin sought refuge in the Savage Land. There Lord Plunder took his son to the mound of Anti-Metal, unaware they were being stalked by the native Maa-Gor and his tribe of barbaric Man-Apes. The Man-Apes slew Lord Plunder, but, as they grabbed Kevin, they were attacked by Zabu, the last of a species of saber-toothed tiger the Man-Apes had hunted to virtual extinction. Immediately forming an empathic bond, Zabu and the boy fled to the Place of Mists, a region where the Man-Apes refused to set foot. The incident soon passed into the Man-Apes' legends, and the boy was given the name "Ka-Zar," which means "son of the tiger." In the Land of Mists, the boy grew to manhood, his saber-toothed companion protecting him from all dangers. From Zabu, Ka-Zar learned the ways of the flora and fauna of the entire Savage Land.
After his father's murder, young Kevin Plunder banished from his consciousness most of the memories of his childhood as a pampered son of nobility and came to think and act like a "savage." Upon reaching maturity, Ka-Zar came into conflict with his brother Parnival, who, calling himself the Plunderer, sought Ka-Zar's half of the medallion in order to gain control of the Anti-Metal. This began a lifelong animosity between them. Influenced by visitors from the outside world, he allowed aspects of his civilized side to emerge. In times of extreme stress, however, he still lapses briefly into savagery.