Fourth Leth was a relatively junior member of the Dark Vanguard. Along with his colleague, Fourth Besh, he was assigned to serve under First Dorn's command at Cademimu V during the New Sith Wars. Fourth Leth chose to specialize in Jar'Kai, and took a pair of red lightsabers into battle.
When Tirien Kal-Di and the 6th Republic Marine Force Reconnaissance Platoon infiltrated the Cademiman Cultural Tower, Besh, Leth, and First Dorn fought them. Leth outlived Besh and killed two Marines, but was himself killed by the Marines during the engagement.