That would be Tor Valum, Sith master. In it, Palpatine says that Vader needs to finish his training and should do so under Sith master Tor Valum, who trained Palpatine. Tor Valum is described as non-human and “Lovecraftian,” and the concept art certainly seems to echo that. I wonder if we could ever see Tor Valum crop up in Star Wars lore after this. Perhaps we will meet Tor Valum someday, somehow after all, just outside of the Rey/Kylo trilogy.

Source: Forbes January 19, 2020 13:41 UTC