Robert Francis Kennedy Jr., also known by his initials RFK Jr., is an American politician, environmental lawyer, anti-vaccine activist, and conspiracy theorist. He is the chairman and founder of Children's Health Defense, an anti-vaccine advocacy group that is a leading proponent of COVID-19 vaccine misinformation, and an independent candidate in the 2024 presidential election. A member of the Kennedy family, he is a son of U.S. attorney general and senator Robert F. Kennedy, and nephew of U.S. president John F. Kennedy and senator Ted Kennedy.

Anti-vaccine activism, also called the "anti-vax" movement, is organized activity to show opposition to vaccination, often designed to increase vaccine hesitancy by disseminating misinformation or disinformation. Although myths, conspiracy theories, misinformation and disinformation spread by the anti-vaccination movement and fringe doctors increase vaccine hesitancy and public debates around the medical, ethical, and legal issues related to vaccines, there is no serious hesitancy or debate within mainstream medical and scientific circles about the benefits of vaccination.