Known as "Heaven's Greatest Warriors", the Four Guardians include:
Black Turtle (Leader)
White Tiger (Best Swordsman)
Red Phoenix (Best Spellcaster)
Along with the Four Seasonal Generals they are the strongest military force in heaven. The guardians come from noble families and are considered highly by heaven. Each guardian has a cardinal direction to guard. It can be assumed that the titles of the Guardians are passed down through noble families.
The leader of the Four Guardians and guardian of the North. The Black Turtle is generally accepted to be the strongest guardian and wields the Black Turtle Sword (a standard sword). The Black Turtle has a small turtle familiar that wears glasses (although it is unknown whether familiars change as the guardians do), however this familiar is not seen throughout the novels, only in the extra informtion at the back of the book. The current Black Turtle is Yoon Doh-hyun and the former was his father, however it is unknown whether the title of Black Turtle is one that is passed down through families.
Wields the Blue Dragon sword, and is the guardian of the East. The familiar of the Blue Dragon is a small dragon called Pa-Ee which donns sharp sunglasses. Although Pa-Ee is not seen in the Manhwa, the current Blue Dragon, Woo-hyun, often conjures a dragon spirit when he fights. The Blue Dragon has, of course, a Blue Dragon sword (a blade-knife-type sword)
The best swordsman within the Four Guardians and the guardian of the West. Traditionally a male, the current White Tiger is the beautiful Ah-hin (a girl). Although it is said that Ah-hin became the heir to the White Tiger because of family issues and her power, she states once that the White Tiger (her and formerly her father) is born immune to spells. The familiar of the White Tiger is a cute tabby cat with sharp eyes and a ribbon and bell around it's neck called Mi-Nyang. Mi-Nyang is the only familiar to make an appearance in the official main story of the Manhwa, although the phoenix familiar appears in a side story. The White Tiger sword is not a sword but a lance or a halbeard. The current White Tiger, Ah-hin, has the most merchandise in the Manhwa that is related to her Guardian Creature (a tiger phone chain, toys in her room, etc.)
The best spellcaster and the guardian of the South. The current Red Phoenix is a Ee-jung but traditionally the Red Phoenix is a woman. Traditionally the attire of the young Red Phoenix is also a females, this is a tradition passed down through the clan of Ee-jung's mother (the former Red Phoenix). The Red Phoenix has a Red Phoenix Sword (a clear, slasher type sword), however, since he is the spellcaster, the Red Phoenix also has a scroll. Since the Four Guardians are fighters and since the current Red Phoenix says so himself (although it may vary from person to person) it can generally be assumed that the Red Phoenix specializes in attack spells.