I love that statue. I spend a part of each day in Athena sitting at the Zacharoplasteo on the square looking at the figure. And you are right, tourists are always asking who he is.
"Constantine Paleologus Dragases emboides all Christian peoples fighting against Muslim Turks. His blood included Greek, Armenian, Anatolian Greek, Serbian, Italian, Bulgarian, Austrian."
He was, as we know, the Despot of Morea at Mistras prior to being the Emperor. The first prayers said for him before he left for Constantinople were said in the main church of my maternal village. I've stood exactly where he stood when those prayers were said. My people were Kesaroi at Mistras and one died on the walls of The City with him.