Mamoru Chiba is one of the main characters in the anime/manga/live-action Sailor Moon. He is also Tuxedo Kamen in the series, and helps supports the Sailor Scouts by either quickly interfering with the enemy causing them confusion or physically helping them out in a fight.
When Mamoru was only a child his parents passed away in a car accident. This blocked his childhood memories of his current lifetime and opened up memories of his previous life as Prince Endymion. After that happened he then soon started to have dreams with a young woman by the name of 'Princess Serenity'. In the beginning of the mangas, Mamoru is shown seeking the Silver Crystal because he believes that the crystal will be able to restore his lost memories. He is also known to have his brainwashed and captured the most.
Mamoru Chiba is the romantic interest of Usagi Tsukino (Sailor Moon). He is shown as stoic, steady and introverted.
A disguise Mamoru created for himself in order to hunt for the Silver Crystal and later assist the Sailor Scouts in battle.
Endymion was the Crown Prince of the planet Earth during the Silver Millennium.
Later in the series, Mamoru is shown as King Endymion, King of the 30th century Crystal Tokyo.
The Moonlight Knight appears only in the anime. After everyone memories were hidden, including Mamoru's he subconsciously still wanted to protect Usagi, so his memories separated from him and concentrated into the Moon Knight. This character could also co-exist in the same space and time as Mamoru.
In the series Usagi and Mamoru are boyfriend and girlfriend. But they were never always friends, in both the manga and anime Mamoru and Usagi were antagonistic towards each other when they first met. Once they did become a couple the both of them become deeply devoted to each other and this is tested many times the mangas, anime and live-action series. After two years of dating with Usagi Mamoru gives her an engagement ring at an airport before he leaves for school to the United States. They do eventually get married. And in the future they have become the King and Queen of the moon and have a child by the name of Usagi but she is often addressed as Small Lady or Chibiusa. In the manga, Mamoru struggles with his identity, first as who he really is, then later if he's in the way of the Sailor Soldiers. He has the power of psychometry, this manifests in his ability to see and read dreams, heal people and monitor the status of Earth.
In the anime they dont develop Mamoru as much but he is show to be more social than the manga version of him. He is also very intelligent and has interests in many different subjects. He also dated Rei Hino for a little while until all the past life identities were revealed.
In the manga many of Sailor Moon's transformations and final victories come as a result of her and Tuxedo Mask combining their powers together. The manga also shows Mamoru as quite, studious, mysterious and stoic. He is usually shown being admired by the student body of his high school because of this.
In the dub version of the anime they didn't make too many changes to his character. He is a bit more extroverted than his original anime counterpart in the voicing. Darien (English name used instead of Mamoru) was more likely to yell and get annoyed than Mamoru of the anime, who was often quiet and distant, even when he was annoyed by something.
In the live action version, Mamoru is much more silent, and dedicated person. He is in search of the Silver Crystal because of amnesia and dreams which told him that the power of the object could bring back his memories. He then donned the Tuxedo Kamen (Tuxedo Mask) outfit and became a jewel thief, in search for the legendary crystal. Once his memories of his past and present lives were brought back to him he assumed his Endymion form to help the scouts and tried to protect Usagi from overusing the Silver Crystal. But it went too far and ended up joining the Dark Kingdom to understand more of the link between the Silver Crystal and Metaria. He then found out that every time Sailor Moon used the Silver Crystal it would give Metaria more power. Endymion then took Metaria into his body before succumbing to its dark power Now evil himself, Dark Prince Endymion, almost killed Sailor Mercury when Sailor Moon was forced to kill him to stop Metaria. He was also revived once Sailor Moon managed to finally control the Crystal's power and destroy Metaria for good.