Captain Selto Durka was feared for his Peacekeeper prisoner ship, the Zelbinion, Rygel knows this very well since he was a former prisoner on the ship and have been tortured by Durka. When Moya's crew find the Zelbinion, in the episode "PK Tech Girl", Rygel discovers the remains of his old nemesis.
However Durkis is not dead, he returns in the episode "Durka Returns", it turns out that the remains Rygel discovered on the Zelbinion, was of a junior officer that Durka killed and dressed like him, in a attempt to avoid capture from the Nebari, that attacked the ship. However the plan did not work and he was captured. In the episode Durka comes aboard on Moya as a Nebri prisoner, and Rygel attempts to build a bomb in order to assassinate Durka. The plan don't work and Durka attempts to take control of Moya, failing that he escapes on the Nebri ship.
In the episodes "Liars, Guns and Money (2): With Friends Like These..." and "Liars, Guns and Money (3): Plan B" Durka re-surface as being the leader of the Zenetan Pirates, after disposing Kcrackic. Durka attempts to eliminate Rygel, however Rygel was prepared for such event and succeeds in killing Durka. Afterwards Rygel carried Durka's head around on a staff.