Gul Zarale was a Cardassian commander responsible for massacres of Bajoran villagers, whose unheroic death at the hands of Li Nalas became the foundation of a resistance legend.
Zarale is not seen, but his death is described in The Homecoming. To the Bajoran people, Li Nalas is the hero who defeated the notorious Gul Zarale in single combat after a long struggle, a story retold throughout the Occupation.
Li gives Commander Sisko the real account. His resistance cell had been ambushed and the few survivors were hiding in the hills when Li went down to a lake and found a Cardassian climbing out of the water after bathing, dressed only in his underwear. The man reached for his weapon and Li shot him. Only afterwards did the others recognise the body as Zarale, who had ordered the destruction of several Bajoran villages.
Li's comrades spread an embellished version, and the legend outgrew him. Sisko argues that Bajor needs the symbol, whatever the facts.