Marc Andreessen

Marc Lowell Andreessen ( an-DREE-sən; born July 9, 1971) is an American businessman, venture capitalist, and former software engineer. He is the co-author of Mosaic, the first web browser to display inline images; co-founder of Netscape; and co-founder and general partner of Silicon Valley venture capital firm Andreessen Horowitz.

He co-founded and later sold the software company Opsware to Hewlett-Packard; he also co-founded Ning, a company that provides a platform for social networking websites. In 2024, he became an advisor to Donald Trump.

As of June 2026, Forbes estimated Andreessen's net worth at $1.9 billion.

Andreessen was born in Cedar Falls, Iowa, and raised in New Lisbon, Wisconsin, which he considered "the sticks". He is the son of Patricia, customer service operator at Lands' End, and Lowell Andreessen, who worked as a sales manager for the seed producer Pioneer Hi-Bred International. He has a younger brother named Jeff. Andreessen has stated that he had problematic relationships with his parents and brother, and that he did not like to talk about them.

Andreessen discovered programming at age 12. In December 1993, Andreessen received his bachelor's degree in computer science from the University of Illinois at Urbana–Champaign (UIUC). As an undergraduate, he interned twice at IBM in Austin, Texas. He worked in the AIX graphics software development group responsible for the MIT X implementation and ports of the 3D language APIs: SGI's Graphics Language (GL) and PHIGS. He also worked as a programmer, earning $6.85 per hour (equivalent of $15.49/hr in 2026), at the National Center for Supercomputing Applications (NCSA) at the University of Illinois. At that time, he became familiar with Tim Berners-Lee's open standards for the World Wide Web, but the World Wide Web browser required advanced programming skills to use.

After being shown the graphic web browser ViolaWWW in late 1992, Andreessen and full-time salaried co-worker Eric Bina worked on creating a browser with integrated graphics that could be ported to a wide range of computers, including Windows. The result was the Mosaic web browser released in 1993. The new web browser led to a 342,000 percent increase in web traffic in a year. Before Mosaic, there had only been 50 websites on the Web, but the number now increased to 10,000, while the percentage of internet users who surfed the Web increased from 1% to 25%.

In the Web's first generation, Tim Berners-Lee launched the Uniform Resource Locator (URL), Hypertext Transfer Protocol (HTTP), and HTML standards with prototype Unix-based servers and browsers. A few people noticed that the Web might be better than Gopher. In the second generation, Marc Andreessen and Eric Bina developed NCSA Mosaic at the University of Illinois. Several million then suddenly noticed that the Web might be better than sex.

Mosaic is often referred to as the first successful web browser. It was also the first browser widely used for both Windows and Mac.

After graduating from the University of Illinois Urbana-Champaign in 1993, Andreessen moved to California to work at Enterprise Integration Technologies. Andreessen then met with Jim Clark, the founder of Silicon Graphics, who had recently exited the firm. Clark believed the Mosaic browser had great commercial possibilities and suggested starting an Internet software company. Soon, Mosaic Communications Corporation was in business in Mountain View, California, with Andreessen as co-founder and vice president of technology. The University of Illinois was unhappy with the company's use of the Mosaic name, so Mosaic Communications changed its name to Netscape Communications, and its flagship Web browser was named Netscape Navigator. Netscape was the first successful commercial web browser (offered for free). It offers a wide variety of clients, servers, development tools and e-commerce applications. It also simplified the interface, increased speed and provided tools to support financial transactions in comparison with its predecessor Mosaic.

Netscape's IPO in 1995 put Andreessen in the public eye. He was on the cover of Time and other publications.

Netscape was acquired in 1999 for $4.3 billion by AOL. Andreessen's hiring as its chief technical officer was contingent on the completion of the acquisition. The same year, he was named to the MIT Technology Review TR100 as one of the top 100 innovators in the world under the age of 35.

After AOL acquired Netscape in late 1998, Andreessen founded Opsware with Ben Horowitz, Tim Howes, and In Sik Rhee. Originally named Loudcloud, the company provided computing, hosting and software services to consumer-facing internet and e-commerce companies. Loudcloud sold its hosting business to EDS and changed its name to Opsware in 2003, with Andreessen serving as chairman. Acquired by Hewlett-Packard for $1.6 billion in 2007, it was one of the first companies to offer software as a service and to attempt cloud hosting.

Between 2005 and 2009, Andreessen and Horowitz separately and together invested $4 million in 45 startups, including Twitter and Qik. The two became well known as super angel investors. On July 6, 2009, Andreessen and Horowitz announced their Silicon Valley venture-capital firm Andreessen Horowitz.

Andreessen endorsed and voted for Bill Clinton, Al Gore, John Kerry, Barack Obama and Hillary Clinton. In 2012, Andreessen donated $100,000 to Republican presidential candidate Mitt Romney. During the 2016 primary season, he endorsed Republican candidate Carly Fiorina, but after Fiorina dropped out of the race, Andreessen switched his endorsement to the Democratic nominee Hillary Clinton, citing the Republican nominee Donald Trump's immigration stance.

In July 2024, Andreessen announced he would donate to super PACs that support Donald Trump's 2024 presidential campaign. During the first half of 2025, Andreessen donated $3 million to MAGA Inc., a super PAC that supports Donald Trump.

Andreessen is a mega-donor to the political superPAC and pro-cryptocurrency advocacy group Fairshake. Andreessen came out against president Joe Biden's re-election bid, saying he feared higher taxes on billionaires and stricter regulations on industries he invests in (cryptocurrency and AI). On Joe Rogan's podcast in November 2024, Andreessen claimed that some cryptocurrency users have been unfairly debanked.

While not officially part of Elon Musk's DOGE, Andreessen has been listed as “a key networker for talent recruitment” at the agency, according to The Washington Post. He has also shared insight about DOGE's plans in various interviews.

Several authors note that Andreessen belongs to a small group of tech leaders who play an increasingly central role not only in the Silicon Valley, but also in the U.S. political life. German journalist Claus Kleber, author of the ZDF documentary Trump und das Silicon Valley – Staatsstreich der Tech-Oligarchen ("Trump and Silicon Valley – coup d'état of the tech oligarchs"), opines that Andreessen's power is only outmatched by that of Peter Thiel, who often works alongside him. Evgeny Morozov, writing for the Spanish El País, notes that Andreessen "reimagines money" for the government, and that the tech leaders (dubbed "oligarch-intellectuals" by Morozov) have power to turn their "interpretive gift [...] into legislative mandate".

Andreessen identifies himself as German-American.

Andreessen married Laura Arrillaga in 2006. She is the founder of the Silicon Valley Social Venture Fund and daughter of Silicon Valley real estate billionaire John Arrillaga. The couple met in 2005, at a New Year’s Eve dinner organized by the former eHarmony CEO. Andreessen considered Arrillaga and her father his replacement family. They got married nine months later. They have one son, who was carried by a gestational surrogate. According to Business Insider, the son was 8 years old in 2023.