Prince Endymion/Prince Darien

Prince Endymion was the prince of the Earth and the previous incarnation of Mamoru Chiba

Manga
In the manga, Prince Endymion resided in the Golden Kingdom in Elysion with his guardians, the Shitennou. He fell in love with Princess Serenity and went to meet with her as often as he could, but the two lovers were found and separated by Kunzite and Sailor Venus.

As in the anime, Prince Endymion fought to defend the Moon Kingdom against Queen Beryl's forces, who in this continuity were led by his brainwashed advisors, the Shitennou. Endymion fell in battle and, in despair, Princess Serenity also killed herself, unwilling to be separated from him.

In the first arc of the manga, as in its anime counterpart, Prince Endymion was kidnapped by Beryl and brainwashed into becoming a minion of the Dark Kingdom.

Anime
In the anime, Prince Endymion was in love with Princess Serenity of the Silver Millennium, and even though it was forbidden they met in secret whenever they could. When he found that Queen Beryl was leading her forces against the kingdom on the Moon, he hurried to get there first to warn his lover and her people. Despite his warning and aid, the Moon Kingdom was destroyed, and both Prince Endymion and Princess Serenity were killed by Queen Metalia.

When Queen Serenity used the power of the Silver Crystal to send her daughter and her court to the future to be reincarnated, Prince Endymion was sent as well. On the present-day Earth, he discovered his past identity at the same time Usagi remembered her past as the Princess. Mamoru could transform into his Prince Endymion form to access its power, usually at the same time Usagi likewise transformed into her Princess form.

In the first season of the anime, Prince Endymion was kidnapped by Beryl and brainwashed into serving her, and fought against the Sailor Senshi. He was later healed by Sailor Moon and sacrificed himself to protect her from Queen Beryl.

Pretty Guardian Sailor Moon
The live-action series mostly followed the manga storyline, especially in that the Shitennou were Prince Endymion's counselors. After Prince Endymion fell in battle, however, Princess Serenity was in such despair that she not only killed herself, but also destroyed the kingdoms on both the Earth and the Moon.

In the present day, both Zoisite and Kunzite remembered their former Master, but while Zoisite worked to help Endymion, Kunzite tried to kill him, blaming him for the destruction of the world. In an attempt to seal Queen Metalia away, Endymion absorbed her into his own body, but ended up being corrupted by the evil force. He became an entity known either as "Dark Prince Endymion" or Metalia Endymion. He was killed by Sailor Moon in order to stop Metalia, but was later revived by the power of the Silver Crystal.

Prince Endymion's uniform in the live-action series was different than those of his other incarnations; instead of being primarily black and red, it was white and teal with gold accents. It also had some design similarities with the uniforms worn by the Shitennou, especially Kunzite's.

Mamoru could willingly transform into Endymion to access more power. Unlike the situation with Usagi and Princess Sailor Moon, there were no apparent conflicts between the two, and at no point did Endymion try to assert control over Mamoru's body for his own purposes.

Mythology
Endymion's name was inspired by the Endymion of Greek mythology. In that story, the Moon goddess Selene fell in love with him, and so asked Zeus if he could be granted a wish. He chose eternal sleep so he would not age and would always be with her.