His family come from Lefkás while he was born in Patras. They put this gravestone up in front of a children’s playground which carries his name. The area is known as Apostolos Santas square. They also have a big sewing shop in town if I’m correct here since it’s an unusual surname.
He took down the German flag from the Acropolis on 30th May 1941 which is what it says on the gravestone.
Big Wikipedia article on him Apostolos Santas.