Last seen on Malachor V
Deceased since 298 BTC
After the death of Darth Malak, the Sith as a whole were in a crisis and much fighting occurred on Korriban. Three Sith Lords, Darth Traya, Darth Nihilus, and Darth Sion formed the Sith Triumvirate, he chose the title Lord of Pain because of his power of keep himself alive with his own anger and pain.
The Sith Triumvirate was known to cause the First Jedi Purge. Darth Sion was killed by the Jedi Exile in the Trayus Academy before the destruction of Malachor V. The Jedi Exile managed to persuade Sion to let go of his anger as he died because he was afraid of letting his power go.