Ossan was a Bajoran Vedek that presided over services in the Bajoran temple on Deep Space 9's Promenade in 2374. During the service, Ossan intoned ancient ceremonial chants designed to properly receive an elaborate ark of the Prophets containing the Orb of Prophecy and Change into the shrine.
After encouragement from Kira Nerys, the mirror universe Bareil Antos, underwent an Orb experience with the Orb of Prophecy and Change overseen by Vedek Ossan. (DS9: "Resurrection")
Ossan was played by John Towey.
His name comes from the script.