Alexandru Librescu

Federation-Cardassian War veteran Alexandru Librescu was among the Starfleet soldiers taken captive during the Dominion War by a group of Cardassians committed to the rebellion against the Dominion. 

When the rebel Cardassians extended the offer to their prisoners on Lessek to join their rebellion, Librescu grudgingly accepted. While taking the offer of Cardassian armor, he sometimes appeared visibly uncomfortable fighting side-by-side with the people he had spent his last war fighting against...and this, in turn, unnerved Thouves Daro, a veteran from the other side. (--The Thirteenth Order)