Robert Francis Kennedy Jr. (born January 17, 1954), also known by his initials RFK Jr., is an American politician, environmental lawyer, author, conspiracy theorist, and anti-vaccine activist serving as the 26th United States secretary of health and human services since 2025. A member of the Kennedy family, he is a son of senator and former U.S. attorney general Robert F. Kennedy and Ethel Skakel Kennedy, and a nephew of President John F. Kennedy.

Kennedy began his career as an assistant district attorney in Manhattan. In the mid-1980s, he joined two nonprofits focused on environmental protection: Riverkeeper and the Natural Resources Defense Council (NRDC). In 1986, he became an adjunct professor of environmental law at Pace University School of Law, and in 1987 he founded Pace's Environmental Litigation Clinic. In 1999, Kennedy founded the nonprofit environmental group Waterkeeper Alliance. He first ran as a Democrat and later started an independent campaign in the 2024 United States presidential election, before withdrawing from the race and endorsing Republican nominee Donald Trump.

Since 2005, Kennedy has promoted vaccine misinformation and public-health conspiracy theories, including the chemtrail conspiracy theory, HIV/AIDS denialism, and the scientifically disproved claim of a causal link between vaccines and autism. He has drawn criticism for fueling vaccine hesitancy amid a social climate that gave rise to the deadly measles outbreaks in Samoa and Tonga.

Kennedy is the founder and former chairman of Children's Health Defense, an anti-vaccine advocacy group and proponent of COVID-19 vaccine misinformation. He has written books including The Riverkeepers (1997), Crimes Against Nature (2004), The Real Anthony Fauci (2021), and A Letter to Liberals (2022).