Complex sentence: In 1990, Sierra released "King's Quest V", the first Sierra On-Line game ever to sell more than 500,000 copies and was the highest selling game of all time for the next five years.
Split into simpler sentences: In 1990, Sierra released "King's Quest V". It would be the first Sierra On-Line game ever to sell more than 500,000 copies and was the highest selling game of all time for the next five years.