Jango Fett was indirectly responsible for arming Asajj Ventress with her signature red-bladed lightsabers in Star Wars: Clone Wars. Fett and Ventress never met, but the latter killed many of Jango’s clones, who, in the Legends continuity, were his pride and joy, representing his Mandalorian legacy. The two legendary warriors were also, ultimately, pawns of Count Dooku and his Sith Master, Darth Sidious. Through the intricate machinations of Dooku, on behalf of Palpatine, Jango provided the Count with a pair of lightsabers which he later gifted to Ventress upon accepting her as his unofficial Sith Apprentice.
The two properties that showcase these events are the 2002 video game, Star Wars: Bounty Hunter, and the 2003 Clone Wars animated series. Both are part of the Legends universe, which was designated the official Star Wars timeline by Lucasfilm before 2014’s continuity revamp. Like the ongoing mainstream canon universe, Legends told a comprehensive story that connected the original and prequel trilogy films and numerous comics, TV shows, video games, novels, and even spinoff movies. Bounty Hunter tells the story of how Jango Fett became the template for the Republic’s Clone Army, tracking down one of Dooku’s apprentices, Komari Vosa, who fell to the dark side and became the leader of the cult-like crime organization The Bando Gora.
Jango defeats Vosa at the end of Bounty Hunter, and the insane dark side user is promptly executed by Count Dooku, aka Darth Tyrannus. Vosa’s now red-bladed lightsabers, whose curved hilts were patterned after Dooku’s weapon, were taken by Dooku following her death. Years later, Dooku would travel to Rattatak in search of a Sith Apprentice, as shown in Clone Wars. A local Rattataki and warlord, Asajj Ventress, proved herself to be more than worthy of Dooku’s teachings, and the Sith Lord gave her Vosa’s lightsabers as a gift to replace her two previous lightsabers, which Dooku destroyed during their brief duel. Thanks to Jango Fett, Vosa’s weapons were passed down to Ventress, becoming weapons of the Sith.
It’s unclear when Komari Vosa built her curved-hilted lightsabers, but she fought Jango Fett’s Mandalorians on Galidraan with a single blue-bladed weapon that had a straight hilt. As the Bando Gora leader, the weapons closely resembled Dooku’s lightsaber, with similar hilts and red blades, generated by synthetic lightsaber crystals. The lightsabers could be linked together, forming a double-bladed lightsaber, similar to Darth Maul’s or Exar Kun’s.
Asajj Ventress used the late Vosa’s weapons to kill numerous Jedi and clone troopers during the Clone Wars, as shown throughout the Legends-era Clone Wars multimedia project. Unlike his Canon counterpart, the Legends-era Jango Fett cared for his clones, and likely would have felt disgusted for inadvertently arming someone who killed so many of them. The connection between Dooku, Vosa, Jango, and Ventress demonstrates the depth of Palpatine’s schemes for galactic dominance. In one fell swoop, Jango Fett removed a liability to Dooku and Sidious, provided them with the ideal Clone Army, and supplied Dooku with weapons for his eventual Sith Apprentice.
Komari Vosa has no counterpart in the canon timeline, so Asajj’s weapons in canon were presumably built by Ventress during her Sith training under Dooku. Ventress, whose background was changed in canon from Rattataki to Dathomiri, must have intentionally built them to reflect Dooku’s curved lightsaber and her fighting style, which blended Makashi and Jar’Kai. In the Legends-era Star Wars: Clone Wars, however, Asajj Ventress got her Sith lightsabers, indirectly, thanks to Jango Fett’s first mission for Count Dooku.