Complex sentence: A Democrat, he is the 54th and current Mayor of Boston and a former member of the Massachusetts House of Representatives who had served from 1997 until 2014, representing the Thirteenth Suffolk district.
Split into simpler sentences: A Democrat, he is the 54th and current Mayor of Boston. He previously served as a member of the Massachusetts House of Representatives, serving from 1997 until 2014 and representing the Thirteenth Suffolk district.