Former PetroChina Chairman Jiang Jiemin

Former PetroChina Chairman Jiang Jiemin

Daniel J. Groshong/Bloomberg

Former PetroChina Co. Chairman Jiang Jiemin, pictured, is the highest-profile official investigated since Chinese President Xi Jinping took over the ruling party in November, vowing to crack down on graft which he said threatened its six-decade hold on power.