Fransu was a Cardassian male who lived in the 24th century.
As a young man, Fransu was a follower of the High Gul of the Crescent Order. However, after the High Gul and 3,000 of his soldiers were put into stasis, Fransu took the bodies of the High Gul and his closest aides and hid them elsewhere, and murdered the remainder of the 3,000. An elaborate funeral was held for the 3,000 in which they were paraded before the Cardassian populace, who were told that the High Gul died in battle. While Terok Nor was under construction, Fransu hid the bodies of the High Gul and his aides in a vacuum sealed compartment on the station.
By then, Fransu had reached the rank of Gul, and was working at Cardassian Central Command. After learning that the High Gul had been revived, Fransu ordered Gul Aman Evek to assume his duties on Cardassia. Fransu arranged to have several drones launched into Bajoran space and blanket the area with white noise, keeping Deep Space 9 from calling for assistance. Fransu took his Galor-class ship CDS Rugg'l to the Bajoran system, and proceeded to attack Deep Space Nine, determined to destroy the High Gul.
One of the attacks left Captain Benjamin Sisko for dead in a corridor, and the High Gul was able to capture Major Kira Nerys. The High Gul took Kira on board the USS Defiant, and was subsequently able to convince Kira to join with him and stop Fransu from destroying Deep Space 9. Doctor Julian Bashir saved Sisko's life, and Sisko sneaked on board the Defiant. Sisko, Kira, and the High Gul were able to defeat Fransu in battle.
Fransu tried to use the High Gul's wife as a hostage to secure the High Gul's cooperation, but the attempt failed when the High Gul's wife told her husband she had lived long enough. Fransu murdered the woman. After the Rugg'l was damaged even further by a Federation task force sent to investigate the loss of communication with Deep Space 9, Fransu was beamed on board the Defiant, and taken into custody.
In the aftermath of the battle, the High Gul committed suicide because he knew that his return would be disastrous for the Cardassian people. Federation officials downplayed Fransu's attack, stating that he was a rogue not sanctioned by the Central Command. (DS9 novel: Station Rage)