Rao is the name of a fictional star featured in the Superman multimedia franchise by DC Comics. It is a red sun located in the Rao system, which currently has no planets revolving around it. The planet Krypton once revolved around Rao prior to its destruction many years ago.
As it emits red solar radiation, Kryptonians cannot develop abilities beyond their natural biology while under Rao's influence. If a Kryptonian were to leave a red sun system for a star system with a yellow sun, they would then develop superhuman physical traits. These traits would diminish once exiting a yellow star environment.
Rao is named for the deity Rao, who is the Kryptonian sun god.