Throughout the entire series, starting when Usagi runs into him, Mamoru serves as Usagi's love (whether directly or indirectly). Mamoru returns this feeling of love quite strongly as the seasons progress. This is in spite of some hardships that occur in the series. However he does go out with Rei in the first series.
As a child, Mamoru is orphaned when his parents die in a car accident. He is alone for most of his childhood; his friend was Fiore, an alien who reappears in the Sailor Moon R Movie. Currently, he lives alone in an apartment in Juubangai.
Mamoru's alternate persona is Tuxedo Kamen who appears when the Senshi need help. In these appearences, Tuxedo Kamen usually gives a motivational speech which prods the Senshi to success. The two main tools of Tuxedo Kamen are his roses and his cane; they are used for attack and defence. In Sailormoon R Mamoru loses his memory, his memories come to the aid of Sailormoon in the form of Moonlight Knight/Tsukikage no Knight. Eventually, his memory is restored and he returns to being Tuxedo Kamen/
In Silver Millenium, he was Prince Endymion of Earth. He was forbidden to love Usagi as she was the moon princess, this resulted in the end of the Silver Millenium.
In Crystal Tokyo he is the King as he is married to Neo-queen Serenity.
An interesting observation about Mamoru is the fact that he has no apparent well paying job that he keeps (he has many single jobs such as working as a waiter at a resort), yet he has a car, a motorcycle, and a big apartment with a large screen TV. Where his roses come from is another unknown phenomenon, though in the Sailormoon Sound Drama (the Sound Dramas are self-parodies), he notes in his diary how he is worried about how roses are becoming more expensive in Japan.
