“Throne for a Loss” is episode four of season one of Farscape.
Whilst the crew are trying to negotiate for some cargo, they are attacked and Rygel is kidnapped. D’Argo takes one of the attackers weapons and starts behaving unusually violently. He normally has a tendency towards violence – he is a warrior after all – but this is out of character.
Rygel is held for ransom, as the kidnappers have got the impression – from him – that he still rules his empire. If he did still rule the massive empire like he used to, Rygel would have access to a lot of money.
This is generally considered to be episode four, but Wikipedia has it down as being episode two.