Clark is former NATO Supreme Allied Commander in Europe and Thunell is the former head of the International Finance Corp., which is the financing arm of the World Bank.
Blackstone, a private equity firm, created Fisterra earlier this year to identify and develop independent power projects. It has a focus on projects in Latin America, Europe and the Middle East.
Clark and Thunell will also serve as senior advisers to Blackstone with a focus on the firm's private equity activities in the energy sector.
Blackstone shares were down 17 cents at $21.42 in morning trading. |