Darth Plaito was a member of Yoda's species and a Sith Lord and temporary secret advisor to Rovaniss during the time of the Hidden War.
Rovaniss discovered Plaito shortly after murdering his parents and showed the already corrupt individual the Dark Side. Plaito disappeared and ROvaniss forgot about the creature until he returned with great depths of knowledge and power. Not wishing to rule, Plaito secretly took on the role of advisor to the Emperor, hiding in the shadows until eventually revealing himself to the other Sith following a test initiated by Rovaniss and himself.
Plaito strongly believed that his most devastating weapon was his image as to the Jedi he was seen as an anti-Yoda and was a reminder that the Dark Side can corrupt anyone.
-- Note --
Plaito will eventually have a black cloak but I'm not going to get any orders soon because MMCB is currently closed down to catch up on orders.