This is one of the statues that makes up the Brewer Fountain in Boston Common. Brewer Fountain was the first public art on the Common, donated in 1868 by Gardner Brewer. It is made up of mythological figures associated with water- Neptune, Amphitrite, Acis and Galtea.
I read that Neptune is the god of the sea in Roman mythology. The Roman style building in the background really compliments this image. The building is across the street from the fountain and it just happened to line up perfectly behind Neptune.
Happy Birthday, Dad!