Darth Tenebrous was the Sith Master of Darth Plagueis. Tenebrous was suspected to have designed the Scimitar, the personal starship of the Sith Lord Darth Maul that was officially designed by engineer and starship designer Raith Sienar.

As with a number of other ancient Sith Lords, Tenebrous served as the namesake of one of the Sith trooper legions of the Sith Eternal, a cult led by Plagueis’ apprentice, Darth Sidious, in 35 ABY. Specifically, the 26th Legion was dubbed the «Tenebrous Legion,» and as Sith history was kept secret from the rest of the galaxy, only Sith Eternal cultists were aware of the name’s significance.

Darth Tenebrous was first mentioned in the new Star Wars canon in the forty-fourth issue of the magazine Star Wars: Build the Millennium Falcon, published by De Agostini on November 4, 2015.

In the Star Wars Legends continuity, Darth Tenebrous was originally introduced in «The Tenebrous Way,» a short story in Star Wars Insider 130, published by Titan Magazines on December 13, 2011. The story was written by Matthew Stover and illustrated by Brian Rood. The character was a male Bith and was also identified as Rugess Nome in the novel Darth Plagueis, written by James Luceno and published in 2012.