The first custom dual lightsabers we see used in the Star Wars universe were created by Exar Kun, a terribly powerful dark lord of the Sith. However, Exar Kun used information contained within a Sith holocron to craft his unique double-bladed lightsaber, indicating that in ancient times, other Sith may have used similar weapons. An interesting thing about this weapon is that Exar Kun chose to keep the Kyber crystals he had used as a Jedi, making him one of the only Sith to use a blue lightsaber.