The Unknown Syrian is Moussa Abadi (1910 - 1997), native of the Jewish quarter of Damascus.
Helped by his French friend and future wife, Odette Rosenstock, he founded a network in the region of Nice, known as the "réseau Marcel", which saved 527 Jewish children from being deported by the Nazis. The network benefited from the protection and the help given by the Bishop of Nice, Paul Rémond.
There is quite a lot about Moussa Abadi on the Web. Why don't we share that information?
Here are a couple of links:
P.S.: Omar, Patrick and Tsedek found Abadi's identity. Did I forget anyone?