He turned out to be a very greedy grave robber who was only interested in stealing the treasure of the Laughing King for himself. He never cared about the safety of Gordon, Lady Penelope and Parker, and so he left them trapped inside and didn't tell International Rescue because he was worried it would jeopardize the funding of his expedition. He even went so far as to say they had all died, but when Scott Tracy confronted him, he confessed it was just a big lie.
After being rescued, he asks about the treasure but an angry Lady Penelope threatens Harold by saying she will order his boss to permanently sack him and stop the funding of his expedition.
Professor Harold was voiced by Matt Zimmerman.
- Harold's voice actor, Matt Zimmerman, was a major voice actor in the classic Thunderbirds TV series.