William E. O'Brien (born 23 February 1959) is a Hong Kong-based American racing driver currently competing in the TCR International Series and TCR Asia Series.
Having previously competed in the Touring Car Series Asia, KL City Grand Prix and Zhuhai Pan Delta Racing Festival amongst others.
O'Brien began his career in 2013 in the Zhuhai Pan Delta Racing Festival, he won the Circuit Hero I, A class three times from 2013 to 2015.
He switched to the Hong Kong Roadsports Challenge for 2015 finishing third in the championship standings that year.
He also raced in the Macau Road Sport Challenge and KL City Grand Prix in 2015.