Zelashiel

"It is extremely difficult to employ in combat and is derived from the teachings of Zelashiel the Blasphemer in the Holocron of Darth Revan"

- Darth Bane, on the Force power drain life

Zelashiel the Blasphemer was an individual from whose teachings the Force power drain life could be derived. Zelashiel's teachings were detailed in the holocron of the Sith Lord Darth Revan and they were later studied by the Sith Lord Darth Bane.