In 2371, he was part of the intelligence operation to expose Legate Tekeny Ghemor's ties to the Cardassian Underground. He captured Major Kira Nerys and altered her to appear to be a Cardassian, Ghemor's daughter Iliana. He then proceeded to pretend to conduct her debriefing from her long-term mission in her father's presence. When Kira continued to resist the story that she was actually Iliana, Entek became more forceful, giving Ghemor the incentive to help her evade using the Underground.
The Star Trek: Deep Space Nine Companion (pp. 179 & 225) notes that the DS9 writers considered making Entek a recurring character and that in an early draft of "Improbable Cause", the Obsidian Order's reason for wanting Garak dead was as punishment for killing Entek.
Entek does not clearly say what his role in the Obsidian Order is, however, while still furthering his plot in this episode, Entek tells Kira (Iliana) she was his best student. This suggests he was an instructor, though it could have been part of the lie.