Erato

Erato was a Tythonian ambassador, he was sent to Chloris to negotiate a trade deal, but instead found himself trapped by Lady Adrasta, who captured him and stole his communication device to prevent any infringement on her trade monopoly.

Biography
Erato was sent to the planet Chloris to try and obtain trading rights between it and his home planet of Tythonus, however, before he could make any contact with the inhabitants he was captured by Lady Adrasta, who steals his communication device and throws him into "The Pit" to maintain her monopoly on the metal in Chloris. Erato manages to transmit a distress signal which is intercepted by the Doctor and Romana, the Doctor rescues him from the pit, but only to discover that the Tythonians have declared war on Chloris due to the missing ambassador, and has dispatched a neutron star to collide with Chloris’ star and destroy the system. It is due to collide within the next twenty-four hours. Working against the odds, the Doctor uses the TARDIS to stabilise the star while Erato weaves a metal covering around it and the danger is neutralised. The Doctor’s last act on Chloris is to push Organon, now one of the de facto rulers, toward a mutually beneficial trade agreement with Erato and the Tythonians. (DW: The Creature from the Pit)

Trivia

 * Erato was the name of the greek muse of lyrical poetry.