"Fear attracts the fearful."

BIO - Vantos Arson was born to an emigrated Witch of Dathomir and her consort on Susevfi, the fifth moon of the seventh planet of the Suarbi system in the Quence Sector. Her mother began developing Vantos' Force abilities while she was still young. A dark side flow was building within her. At age five, her parents fled back to Dathomir with such urgence that she was left behind. Living in squalor on the outskirts of the colonists port of Yumfla, she was taken in by a group of Force users called the Jensaarai. The teachings of this reclusive Jedi sect are traced back to the tutelage of a Dark Jedi named Nikkos Tyris. Despite their sinister heritage, the philosophies of this Force cult have evolved over the decades to take on a defensive orientation. Their fighting style utilizes a technique of holding their lightsabers upside-down. Vantos spent the next fifteen years learning the skills to become a Jensaarai Defender, the equivilant to a Jedi Knight within their order. At the age of twenty, the dark side flow from her childhood swelled up inside her and she sought vengence against her parents for abandoning her. The Jensaarai pleaded with her not to go; that it was against the upbringing they gave her, but she could not ignore the dark side drawing her away. On her way to Dathomir, her ship, the Sonic Banshee, mysteriously crash landed on the planet Korriban. She doesn't know how she came to be in the system, but her search for help led her to a dark valley where she found a man who called himself Darth Morbia. He convinced Vantos to become his apprentice, and took her to his working chambers on the planet Tartarus. There he trained her in the Sith arts and increased her Force abilities tenfold. Her new master also showed her a datacard with information on a mercenary named Arden Lyn. He told Vantos that the mercenary had failed the former Emperor and would pay for her failure, but not before she helped them in their plan to rebuild the Empire. Arden Lyn was tricked into taking Vantos as her apprentice in the fighting art of Teras Kasi. With such a fierce and ferocious looking apprentice to mold, Arden felt like a true threat again. Vantos Arson's skills excelled so rapidly, that only a year and a half after her training had begun, her master felt she was ready to take her Sith name. She took the name Darth Thenno. Her individual fighting skills were unmatched by anyone else in the galaxy. The deadly precision she exuded with her black lightsaber, was so quick and accurate, that sometimes it could not be detected by the eye. Her dedication as a Sith Witch demands that her only purpose is to serve her master.
She has trained to feel no pain, to have no fear, and to give no mercy. She has learned there is no challenge for a Dark Lady of the Sith.

Vantos = a first name used by Lucas in the rough and first drafts of A New Hope. the character was eventually not used.

Arson = the crime of maliciously setting fire to property

Thenno = variation on the word Sthenno = the name of one of the three Gorgons that guarded the entrance to the underworld. literally means "forceful."
I really like the implications of this name. not only does the base name Sthenno almost have the word Sith in it, but the meaning of forceful can be taken to be "full of the Force."

the black lightsaber was just to be different from the Sith Lords always having red sabers. black was chosen because she is the bad guy, and bad guys wear black. now this story is science fiction, so you just have to ignore the fact that a saber made of light can be black, which is the absence of light.