Stephen Terrill/Jonathan Rex aka
Appearing in the boys' first adventure, Stephen Terrill was the original owner of Terror Castle. A star in silent movies, he was able to appear as almost any creature onscreen, providing audiences with genuine thrills of horror. Unknown to the world, however, he had a squeaky voice and lisped, which was revealed when he performed in his first talking movie role. After being totally humiliated because of his speech impediment, he was unable to find additional work and soon found himself almost bankrupt. With the threat from the bank of repossessing his castle, he determined that his castle would never belong to anyone else. He went for a long drive along the seashore, never to return. His car was found in the water, and he was presumed to have died in the accident. When his castle was searched after his death, a note was found in which Terrill pronounced a curse on his castle that it would be haunted forever.
Terrill had, of course, not perished in the car accident. Prior to his disappearance, he had established a second identity for himself as Jonathan Rex, the business manager for Stephen Terrill. As Jonathan Rex, Terrill was able to speak in a sinister whispering voice (hence the name "The Whisperer") and was able to be a more assertive character. After Terrill's disappearance, Jonathan Rex raised parakeets and continued to save money so that he could buy Terror Castle. He also ensured that others who might buy the castle were frightened away from the place so that Terror Castle remained untouched by the outside world.
After the Three Investigators decided to investigate Terror Castle as a potential haunted house, Terrill/Rex tried many different tactics to keep them away from the castle's secret, but the boys proved tenacious in their pursuits, finally unmasking Rex and his friend Charlie Grant as the ghosts of the castle. Although Grant and Terrill were not true villains, they gave the Investigators a few good scares in Terror Castle.