Tuxedo Mask is one of the more complicated characters of the series as he is Darien, Tuxedo Mask, Moonlight Knight ( more or less =), and Prince Darien. In general he is an ally of the Sailor Scouts, but he does have his own interests, as he tells Serena that nothing will stop him from gathering the Rainbow Crystals. His trade-mark is a single red rose... thrown in battle. It has been said that it signifies his love for Serena. The Moonlight Knight is Darien's soul trying to save his true love.
As Darien he is an independant college guy who lives in an apartment. He dates Raye every so often, and has a rather unpleasant relationship with Serena who he lovingly calls "Meatballhead". This relationship turns completely around when Darien and Serena find out who they really are.
As Prince Darien (1000 years ago) he was to marry his true love, Princess Serena. When the Negaverse attacked he tried to save her but the forces were too great and they both died. His soul, along with those of the other scouts was sent to earth to be with his true love.