Marc Lowell Andreessen (born July 9, 1971) is an American entrepreneur, investor, and software engineer.
He is the coauthor of Mosaic, the first widely used Web browser; cofounder of Netscape; and cofounder and general partner of Silicon Valley venture capital firm Andreessen Horowitz.
He founded and later sold the software company Opsware to Hewlett-Packard. Andreessen is also a cofounder of Ning, a company that provides a platform for social networking websites. He sits on the board of directors of Facebook, eBay, and Hewlett Packard Enterprise, among others. A frequent keynote speaker and guest at Silicon Valley conferences, Andreessen is one of only six inductees in the World Wide Web Hall of Fame announced at the First International Conference on the World-Wide Web in 1994.