John C. Martin, who became a billionaire by developing and marketing a daily single-dose pill that transformed H.I.V. into a manageable disease and who popularized another drug that cures hepatitis C, died on March 30 in Palo Alto, Calif. He was 69.

His death, in a hospital, was confirmed by Gilead Sciences, based in Foster City, Calif., where he was chief executive from 1996 to 2016 and executive chairman from 2016 until he retired two years later. The cause was head injuries suffered the day before, when he fell on a sidewalk while walking home in Old Palo Alto, according to the Santa Clara County medical examiner.

A chemist who rocketed from research director to chief executive of Gilead in six years, Dr. Martin turned a struggling pharmaceutical firm with a staff of 35 into a $100 billion company based in Foster City, Calif., with some 12,000 employees.

Gilead jolted the industry with several major scientific breakthroughs, beginning with the development of the first anti-influenza pill, Tamiflu, which the company licensed to the Swiss drugmaker Hoffman-La Roche in 1996. Its advance against hepatitis C came in 2014, with the marketing of Sovaldi, which has been said to cure 90 percent of patients with that liver virus.

Gilead’s work on H.I.V. began to bear fruit in 2004, when its Truvada was approved to treat the virus; the drug went on to gain approval as a means to prevent H.I.V. infection in 2012.

The company’s biggest advance on the H.I.V. front came in 2006, with Atripla, which combined Truvada with Bristol-Myers Squibb’s Sustiva in a single pill, replacing as many as 32 separate medications that some patients were taking daily to treat the virus, which can lead to AIDS.

The single-pill treatment was meant to be more than a convenience. By making it easier for patients to self-medicate, they were more likely to take the full doses that were prescribed, reducing the risk that they could become breeding grounds for drug-resistant strains of the disease.

During Dr. Martin’s tenure, Gilead also created remdesivir in 2009, which proved ineffective in its original mission, to treat hepatitis C and other viruses, but which turned out to be a therapeutic weapon during the Covid-19 pandemic.

While the company’s annual revenue soared past $20 billion and its products were hailed as medical miracles, the federal Department of Health and Human Services claimed that Gilead had infringed government patents in making Truvada. (That case is still pending.) The company also drew fire from state and federal regulators over the prices it charged — $1,000 a month for Sustiva and $1,000 for each hepatitis pill.

Dr. Martin defended Gilead in an opinion article in The Wall Street Journal in 2017. He argued, among other things, that high prices for successful products were needed to subsidize future research.

The company’s defenders also pointed out that Gilead had donated drugs in some cases and that it had partnered with local manufacturers in developing countries to produce discounted generic versions of some treatments for H.I.V. and hepatitis C.

“John’s legacy,” Daniel O’Day, the company’s chief executive, said in a statement, “will be felt for generations to come, living on through the scientific progress made under his leadership and the programs he championed that expanded access to medications for people around the world.”

John Charles Martin was born on May 7, 1951, in Easton, Pa., the son of Tellis Alexander Martin, a chemist for Bristol-Myers, and Janet (Sacks) Martin, who taught chemistry, physics and computer literacy at a prep school in Indiana.

Mr. Martin earned a bachelor’s degree in chemical engineering from Purdue University, where he met Rosemary Carella at a party; they married in 1977 and each earned a master’s degree (his in business administration and marketing) from Golden Gate University in San Francisco. He later received a doctorate in organic chemistry from the University of Chicago.

After working at Syntex Corporation, another drugmaker, from 1978 to 1984, Mr. Martin was director of antiviral chemistry at Bristol-Myers Squibb until 1990, when he joined Gilead.

As chief executive, he and John Milligan, who would become his successor, engineered the $11 billion takeover of Pharmasset, a developer of antiviral drugs, in 2012. In addition to running Gilead, Dr. Martin was president of the International Society for Antiviral Research from 1998 to 2000.

His marriage to Ms. Martin ended in divorce. Among his survivors are their son and daughter, his three siblings and his partner, Lillian Lien-Li Lou, who was listed in a recent filing as the secretary-treasury of the John C. Martin Foundation, whose stated mission is to improve health care for medically-underserved populations.