Along with Joe Hayes, George Johnson was sent by Jackson Foster to find out whether or not the rumors about the Gill Man in the Amazon were true, and, if so, to capture him. He and Joe hired Lucas to take them to the Black Lagoon aboard the Rita II, where they made two attempts to capture the creature. The first attempt, in which Joe went underwater in a diving suit, failed and resulted in Joe's arm being broken. George came up with the idea for the second attempt, which involved dynamiting the entire lagoon. The plan worked and he and Joe returned to Florida's Ocean Harbor Oceanarium triumphant.
He is presumably unrelated to the Dr. Johnson who would pursue the Gill Man years later.