Marc Andreessen, born 9 July 1971, is an American entrepreneur, investor and software engineer best known for co-authoring the first widely used Web browser, Mosaic, as well as co-founding Netscape Communications and Silicon Valley venture capital firm, Andreessen Horowitz.

As a student studying for a degree in computer science at the University of Illinois, Andreessen became a part-time assistant at the National Center for Supercomputing Applications (NCSA) where he became familiar with Berners-Lee’s open standards for the World Wide Web. Together with Eric Bina and colleagues including Larry Smarr and Joe Hardin, he created a browser with integrated graphics that would work on a range of computers.

Having co-created the influential Mosaic Internet browser, he co-founded Netscape, which later sold to AOL for $4.2 billion. He is now a Co-Founder and Partner at Andreessen Horowitz, a venture capital firm that provides seed, venture and growth-stage funding to technology companies. The firm has $2.7 billion under management across three funds, with portfolio holdings that include Airbnb, Actifio, Box, Fab, Facebook, GitHub, Jawbone, Pinterest, Platfora, Quirky and Twitter. Andreessen serves on the boards of eBay, Facebook, Glam Media, Hewlett-Packard, Bump, Kno, Rockmelt and TinyCo.