Mage Clef, also known as the Master Mage or Guru Clef, is a central figure in the land of Cephiro, serving as its most powerful magician and the primary consultant to the Pillar. Despite appearing as a young boy, he is over seven centuries old, with his youthful looks belying his vast age and experience. He carries a large staff which houses his summoned magical creature, Fuhla, and his hair is a distinctive shade of purple.

Clef possesses a personality that balances a strict and often short-tempered demeanor with a deeply compassionate core. While he can project the image of a fussy and dignified advisor, his true motivations are rooted in a gentle and protective nature, especially concerning the well-being of the people of Cephiro. He is a man of few words, preferring to be succinct and direct, and he greatly values silence and careful planning over reckless action. One of his most significant traits is a profound sense of guilt over the events of the first series, as he concealed the full truth of the Magic Knights' mission from them, which led to their pain and hardship.

In Magic Knight Rayearth 2, Clef's role becomes more active and physically demanding. Following the death of Princess Emeraude, the former Pillar, Cephiro begins to crumble and becomes vulnerable to invasions from neighboring worlds. Clef dedicates himself to protecting the land, using his immense power to surround the crumbling palace with a powerful barrier to guard the refugees within. This task pushes him to his limits, and he is shown expending vast amounts of his life force to maintain the palace's defenses, sometimes to the point of near-collapse. He takes on the role of a strategist and mentor to the returned Magic Knights, guiding them as they face these new threats.

His motivations in this second arc are heavily driven by his sense of duty and his lingering regret over past mistakes. Upon the Magic Knights' return, he apologizes to them for misleading them before. He encourages them to fight for themselves and to find a way to return home, rather than fighting for Cephiro itself. A key part of his development is his growing doubt about the fundamental system of the Pillar, a system that demands the ruler sacrifice their personal happiness for the sake of the land. His ultimate goal aligns with the knights' new purpose: to prevent the tragedy that befell Emeraude and Zagato from ever happening again.

Clef's key relationships are central to his character and his past. He was the former teacher of several pivotal figures, including the tragic High Priest Zagato, the wandering swordsman Lantis who is Zagato's younger brother, and the ambitious sorceress Alcyone. His history with them is a source of personal pain and conflict, especially as his former students ended up on opposing sides. He shares a close and trusting bond with Presea, the Master Weaponsmith, who harbors unrequited romantic feelings for him. He also develops a unique bond with the Magic Knights, particularly with Umi, with whom a romantic subplot is hinted at in the anime adaptation. Later, he takes the young monster summoner Ascot under his wing as a student.

As a master of magic for over seven centuries, Clef's abilities are vast and varied. He specializes in multiple schools of magic, including summoning, attack, and defensive spells. His known spells include Accept, which awakens the magical powers in others; Clefto, which summons a magical creature to fight for him; Cresta, which creates a powerful magical barrier to nullify enemy attacks; and Thunders, which calls down a powerful bolt of lightning to strike foes. In the second season, he demonstrates the immense power and risk of his magic when he nearly loses his life using a powerful spell to transport the Magic Knights back from a dangerous dimension.