A validator in KERI and ACDC is anybody that wants to establish control-authority over an identifier, created by the controller of the identifier. Validators verify the log, they apply duplicity detection or they leverage somebody else’s duplicity detection or apply any other logic so they can say “Yes, these are events I can trust”.
During validation of virtual credentials for example, a verifier checks to see if a verifiable [credential](credential) (VC) has been signed by the controller of this VC using the applicable verification method.