Vongerella

In the aftermath of the Yuuzhan Vong War, a female Force-sensitive Yuuzhan Vong was seduced and trained in the dark side of the Force.

Most of the activities of this dark Jedi were unknown, but it was known that she corrupted the Jedi Knight Daye Azur-Jamin. Hiding in the Cloak of the Sith region, he then managed to capture Kyle Katarn who was investigating rumors of a reemergance of the Sith.

Kyle was rescued by a team put together by Jan Ors, Mara Jade Skywalker and Jaden Korr and the cyborg Daye was turned back to the light. He then revealed not only the presence of this Force-sensitive Yuuzhan Vong, but also that she had a master. This master was suspected to be Lumiya, Dark Lady of the Sith.

Behind the scenes
This Dark Jedi was mentioned in an adventure seed in the Dark Forces Saga. She has no official name but was dubbed Vongerella on the Jedi Council Forums.