Complex sentence: However, he continued to be very influential as one of president Suharto's closest advisers throughout the rest of the 1980s and worked closely with the president until Suharto resigned from office in 1998.
Split into simpler sentences: However, he continued to be very influential as one of president's most trusted advisers throughout the rest of the 1980s. He worked closely with the president until Suharto resigned from office in 1998.