One of Silicon Valley's most powerful venture-capital firms, Andreessen Horowitz, is adding former Treasury Secretary Larry Summers to its team.

Summers, who served as Treasury Secretary in the Clinton Administration, president of Harvard and then director of the Obama White House National Economics Council until leaving at the end of last year, will join Andreessen Horowitz as a part-time special adviser, the firm said.

The firm is looking to Summers for global and markets expertise more than his experience in Washington, said co-founder Marc Andreessen.

Summers' precise role will evolve over time, Andreessen said, but he sees Summers helping firms develop strategies. It really matters how you approach the Chinese market, Andreessen said, and Summers has done extensive work there.

Other Silicon Valley venture firms have tapped high-profile former government officials for roles. Former Vice President Al Gore is a partner at Kleiner Perkins, joining former secretary of state Colin Powell, who is a strategic limited partner at Kleiner.

The position brings Summers back in the professional orbit of Facebook chief operating officer Sheryl Sandberg, who served as his chief of staff while he was Treasury Secretary. Facebook is one of Andreessen Horowitz's most famous portfolio investments, along with companies such as gaming network Zynga, which is expected to file for an initial public offering later this week.

Andreessen Horowitz, launched in 2009, has quickly become one of Silicon Valley's most prominent firms. It has become known for paying top dollar for investments in promising companies, particularly in the consumer-Internet area.

(Reporting by Sarah McBride, editing by Bernard Orr)