Gerlun was a member of the Malevolence, a cult of Dark Jedi living in Andeddu's Keep on Prakith. In 137 ABY, Darth Wyyrlok III appeared at the Keep to learn Darth Andeddu's secrets and use them to aid Darth Krayt, the Dark Lord of the Sith. Gerlun and his fellow Dark Jedi confronted the Sith Lord. They were no match for Wyyrlok's mastery of the Force and, under the influence of a Force illusion, Gerlun struck down Demtri. Soon after, Darth Wyyrlok spared Gerlun but killed the rest of the group using Force lightning.
Wyyrlok forced Gerlun to guide him to Darth Andeddu's tomb. Once inside, Darth Andeddu's holocron tried to convince Wyyrlok to place the holocron on Andeddu's body, but Wyyrlok refused. Attempting to avenge himself on Wyyrlok, Gerlun used the Force to grab the holocron and placed it on the body. When he did, however, his life was sucked out of him and Darth Andeddu was reanimated before also being destroyed.