Marc Lowell Andreessen (born July 9, 1971) is an American businessman, venture capitalist, and former software engineer. He is best known as co-author of Mosaic, the first web browser to display inline images; co-founder of Netscape; and co-founder and general partner of the Silicon Valley venture capital firm Andreessen Horowitz. He also co-founded and later sold the software company Opsware to Hewlett-Packard, and co-founded Ning, a platform for social networking websites. In 2024, he became an advisor to Donald Trump. As of June 2026, Forbes estimated his net worth at $1.9 billion.
Early life and education
Andreessen was born in Cedar Falls, Iowa, and raised in New Lisbon, Wisconsin, which he considered "the sticks." His mother, Patricia, worked as a customer service operator at Lands' End, and his father, Lowell, was a sales manager for seed producer Pioneer Hi-Bred International. He has a younger brother, Jeff. Andreessen has said he had problematic relationships with his parents and brother and preferred not to discuss them.
He discovered programming at age 12. In December 1993, he received a 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, working in the AIX graphics software development group responsible for the MIT X implementation and ports of 3D language APIs, including SGI's Graphics Language (GL) and PHIGS. He also worked as a programmer at the National Center for Supercomputing Applications (NCSA), earning $6.85 per hour (equivalent to $15.49 in 2026). At NCSA, he became familiar with Tim Berners-Lee's open standards for the World Wide Web, but the existing browser required advanced programming skills.
After seeing 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. Mosaic led to a 342,000 percent increase in web traffic in a year; before Mosaic, there were only 50 websites, but the number grew to 10,000, and the percentage of internet users who surfed the Web increased from 1% to 25%. Mosaic is often called the first successful web browser and was the first widely used on both Windows and Mac. The NCSA refused to give the Mosaic team credit for their contribution, so a disillusioned Andreessen left the center in 1994.
Netscape
After graduating in 1993, Andreessen moved to California to work at Enterprise Integration Technologies. He then met Jim Clark, founder of Silicon Graphics, who had recently left that firm. Clark saw commercial potential in Mosaic 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 objected to the use of the Mosaic name, so the company changed its name to Netscape Communications, and its flagship browser became Netscape Navigator. Netscape was the first successful commercial web browser, offered for free, and it simplified the interface, increased speed, and provided tools for financial transactions compared to Mosaic.
Netscape's IPO in 1995 put Andreessen in the public eye, including a cover of Time. Netscape was acquired by AOL in 1999 for $4.3 billion, and Andreessen's hiring as chief technical officer was contingent on the deal's completion. That year, he was named to the MIT Technology Review TR100 as one of the top 100 innovators under 35.
Opsware
After the AOL acquisition, 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 as chairman. Hewlett-Packard acquired Opsware for $1.6 billion in 2007. It was one of the first companies to offer software as a service and to attempt cloud hosting.
Andreessen Horowitz
Between 2005 and 2009, Andreessen and Horowitz separately and together invested $4 million in 45 startups, including Twitter and Qik, becoming known as super angel investors. On July 6, 2009, they announced their venture-capital firm Andreessen Horowitz. It began with $300 million in initial capitalization and grew to $2.7 billion under management within three years. By 2012, its portfolio included Facebook, Foursquare, GitHub, Pinterest, Twitter, and Honor Technology. In 2021, Business Insider noted that successful IPOs cementing the firm's reputation included Okta, PagerDuty, Pinterest, Accolade, Slack Technologies, Lyft, DigitalOcean, and Coinbase.
Andreessen and the firm have shown interest in cryptocurrency. In 2021, they launched a $2.2 billion crypto-focused fund, followed by a $4.5 billion fund in 2022. Notable crypto and NFT startups in their portfolio include Alchemy, Dapper Labs, Avalanche, OpenSea, Solana, and Yuga Labs. In 2023, the firm launched the American Dynamism fund, focusing on hard tech sectors serving national interest, including space, defense, manufacturing, and robotics, backing companies like Hadrian and Castelion. In 2024, they launched the American Dynamism Engineering Fellows Program and an annual summit.
Other activities and influence
Beyond his ventures, Andreessen has been a prominent voice in technology. He co-founded Ning, a social networking platform, and has served on boards of companies like Facebook and eBay. He is known for his 2011 essay "Why Software Is Eating the World," which argued that software companies would disrupt traditional industries. He has also been an active investor in Artificial intelligence startups, reflecting his belief in the transformative potential of Machine learning and Deep learning. His firm has backed AI companies such as OpenAI and Anthropic, and he has spoken publicly about the importance of Generative AI and Large language models. Andreessen's influence extends to policy, as seen in his advisory role to Donald Trump in 2024, and his writings on technology and society. He remains a general partner at Andreessen Horowitz, which continues to invest in a wide range of technology sectors.