Billions of people from Earth's past were resurrected to live on Riverworld.
Most of the resurrected awaken in a body equivalent to that of their 25-year-old selves, in perfect health and free of any previous genetic or acquired defects. All heart disease, tooth decay, and blindness are gone, and all amputated limbs are restored; whereas certain neurological impulses (for instance, curiosity or chemical addiction) remain intact. These bodies do not age, after a physical 25 years, and can regenerate nearly any non-fatal injury, including dismemberments and blindings. The new bodies are completely free of infection and seem resistant to it (albeit in the absence of hostile bacteria or viruses on the Riverworld). Initially hairless, the bodies grow cephalic hair and pubic hair at a normal rate. Men do not have foreskins or grow facial hair; whereas women have intact hymens. It is impossible to conceive children on Riverworld.
Anyone who died at an age younger than 25 assumes a body equivalent to that lesser age, which then ages at a normal rate before stopping at 25. No one who was less than five years old at death is resurrected on the Riverworld (it has since been learned that children under the age of five were resurrected on another planet, Gardenworld). Should an individual die, they are resurrected elsewhere along the banks of the river. Some people even use this process to travel, though there is a limit to the number of resurrections available to each person.
Because all the languages of mankind are represented in Riverworld, Esperanto has spread as a common tongue.
Many people have had their characters change as a result of this cosmopolitan setting. During the early history of Riverworld, the tormented, drug-addicted Hermann Goering, who had been a mass murderer on Earth, made a considerable alteration and ended up as a missionary of the peaceful Church of the Second Chance. Many people have recreated their Earthly societies, resulting in a wide array of diverse nation-states on Riverworld.