Background and career
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. The NCSA though refused to give the Mosaic team credit for their contribution, so Andreessen, disillusioned, decided to leave the center in 1994.
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 Horowitz began with an initial capitalization of $300 million; within three years the firm grew to $2.7 billion under management across three funds. In 2012, Andreessen Horowitz's portfolio holdings included Facebook, Foursquare, GitHub, Pinterest, Twitter and Honor Technology. In 2021, Business Insider notes that successful IPOs that have cemented Andreessen Horowitz's reputation include Okta, Inc., PagerDuty, Pinterest, Accolade, Slack Technologies, Lyft, DigitalOcean and Coinbase. Both Andreessen and the firm have an interest in cryptocurrency. In 2021, the firm launched a $2.2 billion crypto-focused fund, which was followed by a 2022 $4.5 billion fund dedicated to crypto and blockchain. Notable crypto and NFT startups in its portfolio include Alchemy, Dapper Labs, Avalanche, OpenSea, Solana and Yuga Labs. In 2023, the firm launched the American Dynamism fund, which focuses on hard tech sectors which serve national interest, including space, defense, manufacturing, robotics. The fund has backed companies like the defense manufacturing startup Hadrian and the hypersonic long-range rocket startup Castelion. In 2024, Andreessen Horowitz launched the 12-month American Dynamism Engineering Fellows Program, which was intended to recruit and train technologists. Also associated with the American Dynamism fund is the annual American Dynamism summit sponsored by Andreessen Horowitz, which gathers startup founders, investors, Members of Congress and Defense Department officials. The summit is officially non-partisan and has partnered with Democratic defense officials like former Deputy Secretary of Defense Kathleen Hicks. On September 1, 2009, an investor group that included Andreessen Horowitz acquired a majority stake in Skype at a valuation of $2.75 billion, which was considered risky. The deal paid off in May 2011 when Microsoft bought Skype for $8.5 billion. In 2010, the firm assisted Silicon Valley attorney Ted Wang in creating the first free standardized seed round financing documents, the Series Seed Documents. Andreessen joined the eBay board of directors in 2008 and served on it for six years. In October 2014, he announced his resignation from the board due to the company's decision to break off its online payments unit PayPal. The decision to cut ties with PayPal was a point of contention between Andreessen and investor Carl Icahn. Icahn advocated for the PayPal split while Andreessen opposed the spin-off, resulting in public disputes. Andreessen was accused by Icahn of putting his own interests in front of what was best for shareholders. Icahn published his argument in an open letter that detailed alleged conflicts of interest in eBay's 2009 sale of Skype to a group of private investors, which included Andreessen's firm. The fund is active in Europe. Despite this, in January 2025, after Donald Trump's election, Andreessen Horowitz closed its London office (its first office in Europe, led by general partner Sriram Krishnan) to pivot back to the crypto market in the U.S. Nevertheless, it has also been developing a strong scout network in Europe, with a focus on AI startups. The fund has invested in the French unicorn Mistral AI, the German AI image generation startup Black Forest Labs and Berlin-based automation platform unicorn n8n, the UK's metaverse unicorn Improbable and insurtech startup Hyperexponential. In July 2025, Andreessen Horowitz led the largest seed round in history for AI startup Thinking Machines Lab, which raised a record $2 billion, valuing the firm at $12 billion. The New Yorker's Tad Friend remarks that Andreessen and Horowitz's leadership styles complement each other, with Andreessen being the visionary chairman while Horowitz is the people-person CEO.
