Gilead Sciences, Inc. is an American biopharmaceutical company headquartered in Foster City, California, that focuses on researching and developing antiviral drugs used in the treatment of HIV/AIDS, hepatitis B, hepatitis C, influenza, and COVID-19. It also develops medicines in therapeutic areas such as oncology and inflammation and cell therapy. In 1987, Michael L. Riordan founded the company under the name Oligogen. The original name was a reference to oligonucleotides, small strands of DNA used to target genetic sequences. Gilead held its initial public offering in 1992, and successfully developed drugs including Tamiflu and Vistide that decade. In the 2000s, Gilead began evolving from a biotechnology company into a large pharmaceutical company, through acquisitions and investments, acquiring several subsidiaries. Gilead is a member of the Nasdaq-100 and the S&P 100. The company has faced criticism over its business practices, including extremely high pricing of drugs such as Sovaldi and Truvada in the United States relative to production cost and cost in the developing world.