For some time, Thevren had served under the leadership of the prosperous smuggler Methlas, even going so far as to act as one of his lieutenants. While Methlas waited to amass a large enough fleet, fifty ships by his account, before turning his group's aims from smuggling to piracy, Thevren did not share his captain's patience.
In the Year of the Deep Moon, 1294 DR, Thevren murdered Methlas and took over as leader of the pirate flotilla. He coordinated a brash, albeit successful, surprise naval assault on the Sembian port cities of Selgaunt and Saerloon. After three days of pillaging, the pirates had decimated Sembia's navy, having sunk every one of their warships. They made away with several vessels as plunder, along with as much treasure and wealth they could take away from the shore.
This magnificent assault made the new pirate commander a famous man among those of his ilk. Thevren's name would long outlive him, however, as during his pirate crew's celebrations, he was poisoned, while drunk in bed, by his lover Thiliana. Although she was also the mistress of Thevren's predecessor, she was not motivated by revenge, but rather thirst for power, as she came to lead the fleet of Dragonisle.