Complex sentence: Together with Seattle retailer Jeff Brotman, he co-founded Costco; and, from 1983 until his January 2012 retirement, Sinegal was Costco's President and CEO.
Split into simpler sentences: Together with Seattle retailer Jeff Brotman, he co-founded Costco. From 1983 until his January 2012 retirement, Sinegal served as Costco's president and CEO.