Title: Sol - "priest"
Zagato is Emeraude's high priest and guard. His official title is "Sol Zagato". It was his duty to protect Emeraude so that she could focus her prayers on keeping Cephiro safe. When the story starts, Zagato has abandoned his post and made a prisoner of Emeraude in a magical bubble. However his motives are not as straight-forward as the Magic Knights initially believe.
Zagato has a number of former members of the castle elite who are loyal to him, including Alcyone (a powerful sorceror), Lafarga (a member of the castle guard), Inouva, and Ascot. He sends them to stop the Magic Knights from awakening their full powers. Zagato is voiced by KOSUGI Juurouta in the anime, who also voiced Lantis in the second season.
Title: Yil (manga) / Masoushi (anime) - "sorceror"
Alcyone is a powerful sorceror whose magic is second only to Clef, her former teacher. Her name can be spelled either Alcyone or Alcione [pronounced "al-see-own-ay"], however I use Alcyone on this site because of her name's origin in Greek mythology. Alcyone is the first antagonist the Magic Knights encounter, as she has been ordered by Zagato to destroy the three girls from another world so that the legend of the Magic Knights never comes true. She is a powerful adversary whose attacks and spells are ice-based. She has the ability to summon beasts from the spirit realm. Alcyone is the most loyal and arguably strongest of Zagato's followers, because she is motivated by love. However Zagato does not return her feelings and uses her loyalty rather heartlessly. In the second season of the anime, Alcyone returns under mysterious circumstances. Alcyone is voiced by AMANO Yuri in the anime.
Title: Ral (manga) / Genwakushi (anime) - "illusionist"
Caldina is an illusionist who enchants others thru her hypnotic dance. She can even cause two friends to fight each other against their will, thru her magic. Her spells cause quite a bit of grief for the Magic Knights when they first encounter her. However she is only providing her services to Zagato for the money he is paying her, and she has no desire to risk her life for him. Caldina is quickly impressed by the loyalty that Fuu and the others show each other in the face of her illusions. In the second season we learn that she is from Chizeta, a small and apparently poor country, which is why she came to Cephiro to make a better life for herself. Although she comes from a foreign country, Caldina speaks in an Osakan accent (!) which is translated rather amusingly in the English dub. Caldina is also very proud of her physical attractiveness, which is a source of amusement because she talks about her "sexy body" in what are often serious, stressful situations! Caldina is voiced by NAGASHIMA Yuko in the anime.
Title: Bal (manga) / Shoukanshi (anime) - "summoner"
Like everyone working for Zagato, Ascot has his own unique reason for fighting against the Magic Knights. In the English translation of the manga he is called a "Palu"/summoner. He can summon beasts from the spirit realm, who are just as friendly as Clef's spirit beasts, but whom the inhabitants of Cephiro think are "monsters". Zagato protected Ascot's "friends" and that is why Ascot fights for him. He seems to be a lonely kid. Umi is the first to recognize that Ascot and his beast friends aren't evil, just misunderstood. Ascot is voiced by TAKAYAMA Minami in the anime.
Dal (manga) / Kentoushi (anime) - Fighter / Swordsman
Lafarga is the chief Dal, captain of Emeraude's Inner Guard. He was Emeraude's bodyguard before Zagato abducted her. Why someone so close to Emeraude is now fighting against the Magic Knights bewilders them. He is a very tough opponent, despite not being a magic user.
Inouva was created by CLAMP, specially for the anime, to be Zagato's right-hand man. He does not appear in the manga. He doesn't seem to do much when we see him conversing with Zagato, but he is the only one who really knows Zagato's goals. He has some hidden abilities, however I can't say anymore without spoiling the last few episodes!