Ros Lai is the daughter of the Nightsister Queen Zalem and an unknown jedi. At a young age her mother was killed by her father and after that she stared to hate the jedi. Being the daughter of a Nightsister and a jedi, she had remarkable force powers. She used her skill to hide herself as a hideous woman named The Rancor and plotted her revenge. In this for she took care of slaves and found the jedi Quinlan Vos who informed her that her mother (somehow alive) was opening a bad bad gate. Together they killed her and took care of the gate. This ruined her plan to take over the Nightsisters. Vos discovered her plan and arrested her. During the Clone Wars she was used to find information on the Nightsisters and the Separatists deals.