darth tanis was an ancient dark lord of the sith who lived at least 4,000 years before the events of "a new hope", as sith accounts from 3966 bby (before the battle of yavin) described kyber weaponry developed by him on the planet malachor. darth tanis is only alluded in "the rise of skywalker: the visual dictionary", where it is revealed that darth sidious' sith eternal cult still had knowledge of tanis thousands of years after his death and had the 17th legion of sith troopers named after him.