In the 1980s Icahn developed a reputation as a "corporate raider" after profiting from the hostile takeover and asset stripping of the American airline TWA. According to Forbes Magazine, Icahn has a net worth of $16.6 billion making him the 26th wealthiest person on the Forbes 400, and the 5th wealthiest hedge fund manager as of February 2017.
In December 2016, incoming U.S. President Donald Trump asked Icahn to serve as a special adviser on financial regulation within his administration. Icahn stepped down from the role in August 2017 in advance of an article in The New Yorker magazine highlighting his conflicts of interests.
Icahn was raised in a Jewish family in the Far Rockaway, Queens section of New York City, where he attended Far Rockaway High School. His father, an atheist, was a cantor, and later a substitute teacher. His mother also worked as a schoolteacher. Carl graduated from Princeton University with a Bachelor of Arts degree in philosophy in 1957 and then entered New York University School of Medicine, but he dropped out after two years to join the army reserves.
Icahn began his career on Wall Street as a stockbroker in 1961; in 1968, he formed Icahn & Co., a securities firm that focused on risk arbitrage and options trading. In 1978, he began taking controlling positions in individual companies. Icahn developed a reputation as a "corporate raider" after his hostile takeover of Trans World Airlines in 1985. Icahn systematically sold TWA's assets to repay the money he borrowed to purchase the company, which was described as "asset stripping." In 1988, Icahn took TWA private, gaining a personal profit of $469 million, and leaving TWA with a debt of $540 million. In 1991, he sold TWA's London routes to American Airlines for $445 million. He formed lowestfares.com to sell TWA tickets and acquired portions of Global Leisure Travel from Ramy El-Batrawi to merge into it.
Icahn launched an unsuccessful $7 billion hostile takeover for 89% of U.S. Steel in late 1986.
In July 2001 Icahn’s Riverdale, LLC loaned Genesisintermedia $100 million in exchange for an option to purchase 2 million shares of the company.
In 2004, after Mylan Laboratories had announced a deal to acquire King Pharmaceuticals, Icahn purchased a large block of stock and threatened a proxy fight over the acquisition. Mylan later gave up its efforts to acquire King.
In 2005, XO Holding announced its intention to sell the wired part of its business for $700 million to its majority shareholder and chairman Icahn; the money would be used to pay back its debts and to buy back its preferred stock for about $600 million from Icahn. Icahn would have then owned the wired business outright, and still own his 60% stake in XO. In spite of Icahn's majority ownership and the board of directors declaring the deal to be in the best interest of shareholders, R2 and other minority shareholders defeated the attempt through the Delaware Court in 2008, which awarded penalties for damages to the business caused by Icahn's self-dealing and/or conflict of interest.
In February 2006, a group led by Icahn (with 3.3% of the stock) and Lazard Frères CEO Bruce Wasserstein proposed the breakup of Time Warner into four companies and stock buybacks totaling approximately $20 billion; they agreed not to contest the re-election of Time Warner's slate of board members at the 2006 shareholders meeting if Time Warner would buy back up $20 billion of stock, nominate more independent members to the board of directors, cut $1 billion of costs by 2007, and continue discussions with the group on the future of Time Warner Cable. In August 2006, he bought stock in the video game publisher Take-Two Interactive, and later increased his holdings to 11.3% in 2009, becoming the company's second largest shareholder.
In January 2007, he purchased a 9.2% stake in Telik, a biotech company engaged in cancer research. By that time he was also the beneficial owner of 6.1 million shares, of WCI Communities. He also owned about 33.5 million shares of Motorola, but in May was refused a seat on its Board of Directors. On February 9, 2007, Lear Corporation's board of directors accepted a $2.3 billion takeover offer from Icahn. That month he also invested $50 million in Motricity, a North Carolina-based provider of mobile content delivery technology. In 2007, Icahn and his affiliates also owned majority positions in ACF Industries, American Railcar Industries, Philip Services, and NYSE-listed Icahn Enterprises, By September he also owned of 8.5% of the business software company BEA Systems. He increased his holdings to 13% in October, two months before Oracle Corporation announced it was purchasing BEA Systems. Beginning in 2007, Icahn gradually increased his stake in biotechnology company Biogen Idec.
Icahn sold his casino interests in Nevada in February 2008, including the Stratosphere, Arizona Charlie's Boulder, Arizona Charlie's Decatur, and Aquarius Casino Resort which were operated through American Entertainment Properties, a subsidiary of Icahn Enterprises. The sale price of $1.3 billion was roughly $1 billion more than he paid for the properties. In March 2008, Icahn sued Motorola as part of his effort to gain four seats on Motorola's board and force a sale of its mobile business. That month, a story about Icahn aired on American news program, 60 Minutes, with reporter Lesley Stahl and he also appeared on Nightly Business Report and discussed his views on proxy fights. In May that year Icahn purchased a large block of shares in Yahoo, and shortly thereafter threatened to start a proxy fight to remove Yahoo's board of directors in response to their rejection of Microsoft's takeover bid. Instead, he forced an agreement to expand Yahoo's board to eleven members, including Icahn and two others of his choice. In June 2008, Icahn launched The Icahn Report, which hosts United Shareholders of America where individual investors can sign up and campaign for shareholder rights. In September/October 2008 Icahn was involved in the rejected attempted purchase of Imclone by Bristol Myers Squibb and in the eventual sale of Imclone to Eli Lilly in an all-cash deal valued at $6.5 billion. In December that year he filed suit against Realogy over a proposed debt swap.
In April 2009, Icahn engaged in a proxy battle for Amylin. In September he offered to buy the shares of XO he did not already own for 55 cents each. He later raised his offer to 80 cents, but it expired. In October he resigned from the board of directors at Yahoo!, and by the following February had reduced his equity stake from a one-time high of 75 million shares to 12 million shares.
Icahn was a director of Blockbuster until January 2010 and the chairman of Imclone, Icahn Enterprises, XO Communications, WestPoint Home, Cadus, and American Railcar Industries. He is a beneficial owner of Adventrx Pharmaceuticals, and Vector Group. Icahn also tried to take over Marvel Comics. Icahn, through a subsidiary of his Icahn Enterprises LP, acquired the Fontainebleau property in Las Vegas for about $150 million in February 2010. In March he was one of a group of lenders who purchased Tropicana Casino and Resort Atlantic City, bringing the company out of bankruptcy for $200 million. Also in March he conducted a failed takeover bid of Lionsgate Films. In May he announced ownership of about 12% of Hain Celestial Group Inc., and the purchase of an 8.54% stake in Lawson Software,
In May 2010 Icahn held 6.9% stake in Mentor Graphics; in July he acquired a 14 percent stake in the company; Mentor then signed a poison-pill provision. In February 2011 Icahn made an offer to buy the company for about $1.86 billion in cash.
In January 2011, Icahn once more made a bid to purchase the remaining shares of the XO Holder common stock. By February he had accumulated a 9.08% stake in The Clorox Company (CLX). On March 15, 2011, Mentor's board issued a strong warning to its shareholders against a proxy action by Icahn.
In October 2012, Icahn purchased a 10% stake in Netflix. In November he was involved in a proxy battle over control of the Oshkosh Corp. board of directors.
In February 2013, Forbes listed Icahn as one of the 40 Highest-Earning hedge fund managers. By April he had accumulated a 9.2% stake in Nuance Communications, Inc. On August 2, 2013, Icahn sued computer giant Dell and its board in an attempt to derail a $24.4 billion buyout bid by the CEO, Michael Dell, in favor of his own rumored forthcoming bid. In 2013 Icahn was an outspoken proponent of Apple; In October that year he held a 4.7 million share position. In October 2013, Icahn acquired around 61 million shares in Talisman Energy prompting shares in the ailing Canadian oil producer to surge. Also that month he sold about 50% of his shares in Netflix for a profit in excess of 800 million in less than one year. In November he acquired a 12.5% interest in Hologic, a medical device and diagnostics manufacturer.
In January, 2014, Icahn bought another half-billion worth of Apple Inc. shares, stating they're "very cheap." Also in January, Icahn proposed to eBay to spin off PayPal, an e-commerce business. This started a proxy fight which was settled by April. By June 2014, had acquired a 9.4 percent stake in Family Dollar. Now the biggest shareholder, he becomes involved in a deal whereby Family Dollar is bought by Dollar Tree for $8.5 billion. He then disposed of about a third of his stake. In October 2014, Icahn took a stake in Canadian energy company Talisman Energy. The company's stock price went down by 71% and he sold his shares two months later.
On May 15, 2015, Icahn made a $100 million investment in the ride-sharing service Lyft. In November 2015, Icahn hired CBRE Group Inc. to market the unfinished resort Fontainebleau Las Vegas to potential buyers. That month he swapped his stake of eBay for the same number of shares in PayPal Holdings. At that time Icahn held a 7.13% stake in Xerox; he was the second-largest investor after The Vanguard Group. In December 2015 Icahn made a qualifying offer to purchase the auto-parts and maintenance chain Pep Boys for $15.50 a share. He also raised his stake in the Houston-based energy company Cheniere Energy to 13.8, making him its largest shareholder. Icahn sold the unfinished Las Vegas casino Fountainebleau, for $600 million in August 2017. 
In January 2016, Icahn held a 4.66% stake in Gannett Co. Inc., and also held shares in Cheniere Energy and Freeport-McMoRan, both of which declined in value. Icahn sold his Apple shares in April 2016, citing concerns about Apple's relationship with China. In August of that year he purchased 10 percent ownership of Herbalife; his holdings in the company were about 19 million shares by October. Also in October Icahn closed the Trump Taj Mahal Casino in Atlantic City, citing a $350 million USD loss over a few years as well as being unable to reach a negotiation deal with union workers on strike. Nearly 3,000 workers lost their jobs. That year he also increased his holdings in the car rental company The Hertz Corporation, after the company's stock price had declined significantly.
In 1979, Icahn married Liba Trejbal, a ballerina from the former Czechoslovakia. They separated in 1993 and divorced in 1999 after years of litigation during which Liba sought to invalidate a prenuptial agreement she had signed prior to their marriage, claiming duress as she was pregnant at the time. Liba originally fought Icahn's offer of roughly $1.5 million a year because he was worth billions at the time and eventually settled for an undisclosed amount. They have two children, one of whom is Brett Icahn.
In 1999, Icahn married his longtime assistant and former broker, Gail Golden. She has two children from a prior marriage.
Icahn endorsed Donald Trump for the 2016 U.S. presidential election. He also announced the formation of a super PAC pledging $150 million to push for corporate tax reform, in particular of inversions, which occur when corporations leave the U.S. to take advantage of lower tax rates elsewhere.
Upon becoming the presumptive Republican presidential nominee, Trump announced that he would nominate Icahn for Treasury Secretary. However, this position went to Steve Mnuchin instead.
Bernie Sanders criticized Icahn's investment operations in Atlantic City, specifically reductions in casino employees' benefits including pensions and healthcare. Icahn disputed Sanders' remarks while acknowledging that the general income inequality issue "is a major problem."
On December 21, 2016, it was announced that Icahn would serve as Special Advisor to the President on Regulatory Reform under President Donald Trump. CNBC reported that Icahn would aid Trump in an "individual capacity" rather than as a federal employee, and that he would not have "specific duties" and therefore would not have to relinquish his business interests while serving as an advisor to Trump. Icahn stepped down from this role on August 18, 2017 citing a desire not to interfere with the work of Neomi Rao as Administrator of the Office of Information and Regulatory Affairs.
When the President had Icahn interview Scott Pruitt during consideration of his nomination as Administrator of the Environmental Protection Agency, Icahn specifically asked Pruitt about his position on the EPA's Renewable Fuel Standard. Icahn has also spoken directly to President Trump and to Gary Cohn about his proposed changes to the ethanol rule. CVR Energy, in which Icahn has 82% ownership, would save $205.9 million a year if Icahn's proposal is adopted.The Sugar Land, Texas oil refinery benefited when President Trump made an exception to his regulation freeze to expand the tax advantage of master limited partnerships. CVR Energy’s stock doubled after President Trump's election, increasing $455 million in value.
According to Forbes Magazine, Icahn has a net worth of $16.6 billion USD making him the 26th wealthiest person on the Forbes 400, and the 5th wealthiest hedge fund manager as of February 2017.
Icahn Stadium on Randall's Island in New York City is named after him, as is the Carl C. Icahn Center for Science and Icahn Scholar Program at Choate Rosemary Hall, a prep school in Connecticut. This organization pays for tuition, room and board, books, and supplies for 10 students every year for four years (freshman-senior), an expense that adds up to about $160,000 per student.
Icahn made a substantial contribution to his alma mater, Princeton University, to fund a genomics laboratory which bears his name, the Carl C. Icahn Laboratory at the University's Institute for Integrated Genomics. He also made large contributions to Mount Sinai Hospital, New York, of which he is a trustee, which in return not only named a building the Icahn Medical Institute designed by Davis Brody Bond, but also, in 2013, renamed the Mount Sinai School of Medicine as the Icahn School of Medicine at Mount Sinai. The genomics institute led by Eric Schadt was also renamed and is now the Icahn Institute for Genomics and Multiscale Biology.
His foundation, the Children's Rescue Fund, built Icahn House in The Bronx, a 65-unit complex for homeless families consisting of single pregnant women and single women with children, and operates Icahn House East and Icahn House West, both of which are homeless shelters located in New York City.
Icahn has received a number of awards, including the Starlight Foundation's Founders Award and its 1990 Man of the Year Award. He was also named Guardian Angel 2001 Man of the Year. In 2004, he was honored by the Center for Educational Innovation – Public Education Association for his work with charter schools. In 2006, he was honored with the 100 Women in Hedge Funds Effecting Change Award for his outstanding contributions to improving education.
In 2010, Icahn joined the Giving Pledge list, pledging to give away more than half his fortune, yet has not decided on the specific beneficiaries.
On January 30, 2016, Icahn donated $1 million for US veterans groups at a Des Moines, Iowa, fundraiser held by Donald Trump.
In 1985 Icahn established Foxfield Thoroughbreds, a horse breeding operation. At that year's Newstead Farm Trust sale run by Fasig-Tipton, he paid $4 million for Larida, a 6-year-old mare and a record $7 million for the 4-year-old bay mare Miss Oceana who was in foal to champion sire, Northern Dancer.
Icahn's Meadow Star won the 1990 Breeders' Cup Juvenile Fillies and was voted the Eclipse Award for Outstanding Two-Year-Old Filly. In 1992, Foxfield ended its racing operation and became a commercial breeder. Having bred more than 140 stakes horses, in 2004 Icahn shut down Foxfield, selling all his mares and weanlings without reserve at the Keeneland Sales November breeding stock auction.