Exar Kun existed millennia prior to Darth Sidious and his Sith apprentice Darth Maul, and he was a Dark Lord of the Sith. The Qel-Droma Epics state that Kun, once a Jedi, fell to the dark side of the Force and became a Sith Lord. He then spearheaded a Sith Empire alongside fellow fallen Jedi Ulic Qel-Droma circa 4000 BBY. The double-bladed lightsaber's origins, according to the Qel-Droma Epics, can be traced back to Exar Kun.
During the Imperial Era, Dryden Vos, a crime lord, possessed a desk with a base consisting of an obsidian slab. This slab had been looted from a Sith temple. The stone featured carved warding spells, and also bore an inscription that declared, "Our temple honouring Sith Lord Exar Kun."
The canon of Star Wars first mentioned Exar Kun in Nexus of Power, a 2016 addition to the Star Wars roleplaying games from Fantasy Flight Games. Kevin J. Anderson conceived the character, who debuted in the Star Wars Legends timeline. Though unnamed, he was initially referenced in the 1994 book Jedi Search before being formally presented in its sequel, Dark Apprentice, also released that year. Anderson was initially conflicted about whether Kun should be a "Dark Jedi" or a Dark Lord of the Sith during the character's development. George Lucas's vote for the latter ultimately decided the matter.
Lee Sandales, the set decorator for Solo: A Star Wars Story, mentioned in the 2018 book The Art of Solo: A Star Wars Story that the obsidian stone used as the foundation for crime lord Dryden Vos's desk on the First Light had been stolen by Vos from Exar Kun's Sith temple. Part of the inscription on the base is visible in the movie, while the remainder can be found in the reference book Solo: A Star Wars Story The Official Guide.
An image of a structure resembling the Temple of Exar Kun from the 2003 video game Star Wars Galaxies is featured in the 2016 book Star Wars: Galactic Atlas. The 2021 book "Scarif and Other Planets in the Outer Rim," which is part of De Agostini's Star Wars Encyclopedia, includes Ralph McQuarrie's rendering of the temple from the 1995 book The Illustrated Star Wars Universe. Both illustrations depict a statue of Exar Kun, but there is no confirmed connection between them.