The Prison Warden is known as the man in charge of the Fire Nation prison the Boiling Rock. He appears in the Avatar: The Last Airbender episodes the boiling rock part 1 and 2. He is known as the uncle of Mai as well who is Zuko's love interest. He is a cruel warden who frankly does not take crap from any of his prisoners as shown with Hakoda of the Water Tribe who is Sokka and Katara's father. He did not get killed he was disposed of by Team Avatar and locked away.
It seems likely that, with Zuko and Sokka's group being his first real escapees, added to Mai's attack on Azula, he wasn't warden for very much longer.
It is later mentioned that he pulled some strings to get Mai out of prison.