Theron's helmet was the helmet of the Argolin leader, Theron.

Theron wore this helmet during the twenty minute war with the Foamasi. After their defeat, it was hung in the main room of the Leisure Hive as a reminder that war causes destruction. It was removed from its place by Pangol, and used by him when he cloned himself using the Tachyon Recreation Generator. In doing this all the clones wore exact replicas of the helm. Unfortunately Pangol's plans were ruined as the clones were not of him but of the Fourth Doctor. Gradually, these images faded, leaving the original helmet worn by the actual Doctor. The original was thrown by the Doctor at the screen of the Tachyon Recreation Generator, causing it to shut down. (TV: The Leisure Hive)

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