Kamen Rider Regad Omega is the form that is accessed by authenticating the Sirius Card with the Zillion Driver.  His real identity is Shuel, Creator of the Desire Grand Prix and the overarching antagonist of Kamen Rider Geats, the fourth Reiwa era installment of the Kamen Rider franchise. He is an enigmatic figure behind Desire Grand Prix and the leader of the Game Masters that control the deadly game for all life.
https://kamenrider.fandom.com/wiki/Suel#Regad_Omega