Lumiya (originally named Shira Elan Colla Brie – yep, you heard that right) was a Legends character from Star Wars comics and novels also known as the Dark Lady of the Sith. If she doesn’t sound cool enough for you yet I should mention one of the weapons she used was a lightwhip.
Lumiya debuted (as Brie) in Star Wars: Coffin in the Clouds comic and her adventures took place during and after the original trilogy Star Wars films. Star Wars 88: Figurehead was the first issue where Brie was referred to as Lumiya. Darth Vader took a serious interest in her career and throughout her long and complicated life she also had interactions with Luke Skywalker and other members of the Rebel Alliance.
Lumiya was featured in the short story Lumiya: Dark Star of the Empire (which can be found in Star Wars Galaxy #3 magazine) and played a large role in several Legacy of the Force novels.
Here’s a pretty cool action figure of her sold as a two-pack with Luke Skywalker.