King is the Fairy King and is a member of The Seven Deadly Sins, his sin is Grizzly Sin of Sloth
King was the ruler of his Country 700 years ago. However at some point, he left his sister Elaine in charge of his country, primarily to guard the Fountain of Youth. This left his sister lonely for centuries until Ban came along and befriended her. King eventually became known as one of the Seven Deadly Sins, however his sin is not currently known.
King is a character created by Suzuki Nakaba as one of the main protagonists of the series Nanatsu no Taizai. No inspiration for King's character is apparent, although author Suzuki Nakaba said that he bases his characters off of people he knows personally in his life.
King's greatest evolution so far would be his coming to terms with Ban. Due to a misunderstanding King wanted to murder Ban but his hatred was resolved when he discovered the truth.
King in his normal state has the appearance of a young boy despite his age. He has reddish-orange hair. However in his transformed form, His appearance changes to an overweight, middle aged grown man with a vague resemblance to his normal form.
King has a somewhat lazy personality which is fitting for his title the Bear's sin of sloth. Although usually not unkind, King will kill without a second thought as shown against Geera and Ban before they came to an understanding.
Although not appearing in this arc, King is mentioned by Gilthunder, who tells Meliodas that King died in the Capital of the Dead.
King is introduced in the flesh near the beginning of this arc. After Meliodas and co. arrived near the Capital of the Dead, Ban had sneaked away to avoid cooking duty. After realizing that Ban was gone, Meliodas, Diane and the others went off to find him. When they did find Ban, they found him in the middle of combat. Diane being the first to recognize the foe as King. Noticing Diane, King flew away immediately. This was due to his big crush that he had on her.
After Elizabeth was captured, Meliodas insists going after her immediately against King's advice. After witnessing Diane hurling Meliodas, Ban and Gowther all the way to Liones Kingdom (where Elizabeth was being held), Kind decided to also assist in the rescue along with Diane. King summons his pet Oslo which had the ability to transport things to a different location. Diane goes through first, but she was so large that she couldn't fit her rear end all the way through, and only her upper half of her body was in Liones while the rest of her body was still with King, who because of this was unable to follow through. Diane asks King to push her butt through, but King hesitates due to his shyness of Diane.
King is shown to be an incredibly formidable opponent, able to deftly maneuver his spear with ease. He is strong enough to overpower a Holy Knight single-handedly. As the fairy king, King has demonstrated a number of unique abilities such as the ability to levitate or fly and the ability to change his appearance and clothes at will. Despite his great power, King is actually very physically weak but made up for the lack of strength with his sacred treasure Spirit Spear Chastiefol.
Chasttiefol is King's sacred treasure. Sacred treasures are immensely powerful weapons wielded by the 7 Deadly sins. With Chastiefol, King was able to effortlessly defeat Geera who was able to fight three of the other Sins at once while they didn't have their sacred treasures, showing just how much more powerful the Deadly Sins are with their sacred treasures. Chastiefol is created from a sacred tree, which is exclusive to King's own Fairy Realm. It can transform into many smaller spears which King can wield without touching them, and can transform into a large pillow or stuffed Grizzly Bear. It is also much harder than steel and even in the event that it is broken, it reforges itself in moments. It has also demonstrated the ability to petrify what it touches into stone. Whether or not this is derived from Chastiefol or King's own power is unknown.