Yeemik was second in command to Klarg at the Cragmaw Hideout. He tortured Sildar Halwinter and when the fearsome five attacked them and his defeat seemed imminent, he attempted to negotiate with the group. Sildar’s life if they killed Klarg so he could become first in command.
The Fearsome Five risked Sildar’s life by attacking anyways, Yeemik slit Sildar’s throat but did not kill him before Haesten could save him.
Yeemik was finally killed by Greg who threw a spear taking his dick off and pinning it to the wall of the cave