Darien hides his identity behind a mask. He shows up to help the Sailor Scouts. Always arriving with some type of quote (kind of like a fortune cookie hehe). After revealing himself and finding out the Sailor Scout's identities he helps to protect Sailor Moon. For a while he did not know who he was and his memories tried to brake through in flashes. During this time he was the Moonlight Knight. 

Tuxedo Mask

Moon Light Knight