Blue Knight

The Blue Knight is a mysterious alien hero appearing in Mew Mew Power. He is of the same race as the Cyniclons, except that his skin is not as pale as theirs. He is introduced at the end of the fourth volume of the manga when he suddenly appears to rescue Zoey during a battle with Dren. He tells Zoey that he "is hers" and that he was "born to protect her".

History
After his first appearance, the Blue Knight reappeared whenever Zoey was in danger—fighting with an unnamed sword and disappearing soon after. As the series progresses, Zoey attempts to learn his true identity, suspecting both Elliot and Wesley at one point, before learning near the end of the series that he is an alternate persona of her boyfriend, Mark. The persona, which had no memory until Mark transformed to protect Zoey in front of her, was created out of his desire to protect Zoey. After his true identity is revealed, the Blue Knight, now knowing he is Mark, goes with Mew Zoey to fight together with the other Mew Mews once. There is it revealed that Masaya/Blue Knight is are both alternate personalities of their worst enemy Deep Blue. The Blue Knight disappears after Mark's transformation into Deep Blue.

Tokyo Mew Mew a La Mode
In Tokyo Mew Mew à la Mode, Mark notes that he no longer possesses the powers he had as the Blue Knight. In the anime adaptation, the Blue Knight is given a larger role, fighting with all of the Mew Mews several times, advising them to the weaknesses of the monsters, and encouraging them.

Trivia

 * In the Mew Mew Power English adaptation, he is one of the few characters whose original name is retained.