Adrasta

Lady Adrasta was the ruler of the lush jungle world of Chloris, where metal in all forms was a rare and prized commodity. Together with her aid, Karela, she had a monopoly on the supply of metals, controlling the planet's very last metal mine, and holding on to power through the Huntsmen and the Wolfweeds.

When Erato, an ambassador from the planet Tythonus, which has a lack of chlorophyll but an abundance of metal, attempted to start trade negotiations, she had him thrown into a pit rather than lose her monopoly. The Fourth Doctor freed Erato, who went on to kill Adrasta by crushing her to death and dissolving her in seconds. (DW: The Creature from the Pit)