Complex sentence: He served as Lord Mayor of Belfast in 1986--1987 and again from June 2000 to June 2001, the first person from the DUP to hold the office.
Split into simpler sentences: He served as Lord Mayor of Belfast in 1986--1987 and again from June 2000 to June 2001. He was the first person from the Democratic Unionist Party (DUP) to hold the office.