Marc Lowell Andreessen (/ænˈdriːsən/ an-DREE-sən; born July 9, 1971) is an American entrepreneur, investor, and software engineer. He is best known as coauthor of Mosaic, the first widely used Web browser; as cofounder of Netscape; and as cofounder and general partner of Silicon Valley venture capital firm Andreessen Horowitz. He founded and later sold the software company Opsware to Hewlett-Packard.