Doctor John Storm was at home when suddenly a giant ape burst in in a state of rage. To protect his master, Storm's dog Rex attacked the gorilla, but miraculously transformed into a beast with a skull like head. Rex saved his master, but the poor dog died shortly thereafter from stress of the attack and transformation.
Storm discovered that during the gorilla's attack, one of his formulas spilled on Rex's food, which he ate. The formula transformed Rex into into a raging, blood thirsty beast. Storm theorized the formula would transform a creature to survive.
At the same time, a raging thunderstorm sent a bolt of lightning which struck a tree sending a limb crashing to the earth in front of Laslo Pevely who was out for a drive. Pevely crashed into the limb and staggered toward Dr. Storm's house. Discovering the accident victim, Storm decided to inject the formula into him because Pevely had developed amnesia from the accident and it would insure his survival.
But John Storm's strange evening wasn't over. Three thugs invaded Storm's house insisting that he assist them in their criminal endeavors. Storm refused and the three thugs beat Storm mercilessly. The amnesiac Pavely was driven to stop the thugs and transformed, his face turning into a skull like visage. The thugs ran, but Pavely chased them down, killing them. Finding Doctor Storm dead, Pavely decided to fight crime as...The Terror.