Marel was an illusionary Cardassian gul who commanded a Galor-class warship in a Romulan holographic illusion in 2370.
In the illusion, Marel and his warship (actually a D'deridex-class warbird) intercepted the Klingon warship, IKS K'Tang, in Sector G17 of the Gamma Quadrant and demanded that they turn themselves over for crimes against the Cardassian Empire. The K'Tang was then destroyed and the Cardassians implicated in declaring war against the Klingon Empire. This would therefore allow the Romulan Star Empire to start expanding into the Gamma Quadrant. (DS9 comics: Hearts and Minds - Prelude & Masters of War).