Ragnar Ágúst Nathanaelsson (born 27 August 1991) is an Icelandic basketball player who plays for Hamar of the Icelandic 1. deild karla. He participated at EuroBasket 2015 as a member of the Icelandic national team. He is a two time Úrvalsdeild Domestic All-First team selection and won the Icelandic Basketball Cup in 2022.