To my people, I'm a hero. To you? I'M THE BAD GUY!!!
His goal is to serve the Knight by protecting the Eastern Fountain and invading the world with darkness, thus making the Darkners the rulers of it. This goal is thwarted, at least temporarily, when Kris seals the Eastern Fountain at the end of Chapter 1.
King shares multiple features with his son, such as the tear-shaped head with a black spade where his eyes should be, a mouth showing his tongue and big teeth, a broad and white/dark grey body, and blue gloves and boots. What differentiates him from Lancer is the three-spiked crown on his head, the enormous mouth (with more square shaped teeth compared to the curved fang shaped ones in the mouth on his face) on his stomach shaped like a blue spade from where a chain comes out when used as a weapon in battle, and the black cape that flies away at the end of the battle. King's right arm can only be seen when he turns around or is carried by the crowd at the end of his battle.
King is a cold-hearted Darkner with little compassion towards his subjects and only considers his own wishes. He appears to be power-hungry, evident by his constant wishes of gaining control of the World along with his following of Knight's plan to capture the three other Kings.
King also displays signs of abuse towards his son Lancer, in which he often neglects him and even uses him as a hostage to gain the upper hand in battle. During the final fight, it is revealed that King's loyalty lies solely with the Knight, and that he'll do anything to avoid failing them; to the point of threatening to kill Lancer if Kris, Ralsei, and Susie do not surrender.
Despite this, King does seem to have some form of care for his son, as when talking to him in his cell, he asks if Lancer was happy. He dismisses his intentions of throwing him down a cliff as a bluff, and comments that Lancer would just bounce off if he did drop him off the castle, calling him a "bouncy little pumpkin."
Long ago, the Card Kingdom was ruled by four kings. However, some time before Kris and Susie enter the Card Kingdom, the Knight appeared. It is implied that King then started working for the Knight's schemes, and that it was the Knight who created the Eastern Fountain at Card Castle. With the Knight's appearance, the three other kings were locked away in Card Castle, and King put himself and Lancer into absolute power over his kingdom.
In the climax of Chapter 1, King makes an appearance as the main antagonist. When the Heroes reach the top of Card Castle, Lancer can be seen attempting to reason with his father. However, King decides to use Lancer as a hostage in hopes of forcing the heroes to surrender. Despite this, Lancer manages to break free from King's grasp, allowing the Heroes to fight back against him.
During the fight, King begins to rant about the Lightners, believing that they left the Darkners alone. However, he insists that the Lightners are no longer necessary for his purpose, as the Knight has already filled that gap. He explains his end goal is to create a world blanketed in darkness and ruled by Darkners.
The heroes manage to defeat King, who then surrenders and "admits" that he never wanted to have a war against the Lightners. Ralsei proceeds to heal King. His speech turns out to be a ruse as he brutally knocks out the Heroes, only for either one of two interventions to occur:
- If any enemy in the game has been defeated by fighting (not counting Jevil, Lancer, or King): Susie distracts King long enough for Ralsei to cast a Pacify Spell on him, thus putting him into deep slumber.
- Otherwise: Lancer and several Darkners arrive in the nick of time to capture King. Lancer declares that "they'd rather have a king that accepts them" instead of the old monarch.
King plays a less major role in Chapter 2, instead being an NPC that can be interacted with in the cells under Ralsei's castle. When interacted with, he asks whether Kris has come to humiliate him, and says that staying in his cell is far less humiliating than being in a kingdom ruled by "The Lightners' little patsy," referring to Ralsei.
Before leaving the room, he asks whether Lancer is happy, with Susie reminding him about his attempt to throw him off the building. King, calmly, mentions that, even if he did throw Lancer off the castle, he'd just bounce back, calling him a "bouncy little pumpkin." Ralsei mentions the nickname being cute, and Susie gets angry, saying that they're done talking with him.
When talked to later after recruiting everyone in Cyber World, he interacts with Queen, and they have a temporary talk. During this talk, King gets angry at Queen's criticism of the "Royal Water Bottle" and her new role as Lancer's mother. Reluctantly, he tells her to do what she wishes, but if he cries, to bounce him for a bit. Before she leaves, King asks her to buy him cashews from the store.
If the party fails to acquire all recruits from Cyber World, King simply comments that they "left [the citizens of the Cyber World] behind" and refuses to interact with the party, only saying "Begone."
The king's attacks generally revolve around moving the box in which the SOUL resides.
- Spade Attack: King launches a series of spades which inflict damage upon contact. They can appear on either the left or the right side of the screen, and move horizontally to the other side.
- Swing Attack: King grapples the box with his chain, and swings it up and down. A line of spades marches from the center left of the screen horizontally to the right, which deal damage on contact. On later turns, the speed of the swinging will increase and the gaps between spades decrease.
- Chain Attack: King launches a series of chains with a spade symbol on top. Their trails are indicated with red lines. On later turns, the rate of the chains increases and the warning before each chain decreases.
- Spiked Cage Attack: King traps the SOUL in a spiked cage which bounces off a set of walls in the shape of a square. The spikes inflict damage upon contact. On later turns, the size of the walls decrease and the cage speeds up.
- Chained Cage Attack: King traps the SOUL in a spiked cage which is dragged by a chain to random positions indicated by a heart. The spikes inflict damage upon contact. On later turns, spades will appear in a fixed grid and also deal damage.
This battle is completely scripted, and attacks always come in the same order:
- Spade Attack I
- Swing Attack I
- Chain Attack I
- Spiked Cage Attack I
- Swing Attack II
- Chained Cage Attack I
- Chain Attack II
- Spiked Cage Attack II
- Spade Attack II
- Swing Attack III
- Chained Cage Attack II
- Chain Attack II
- Spiked Cage Attack II
- Swing Attack III
- Spade Attack II
Immediately after the 15th attack, the battle ends. King's Defense drops by 5 after his 12th, 13th, and 14th attacks (for a total of -15 DF on the party's last turn).
As King cannot be reasoned with according to his flavor text, sparing him is not an option. Therefore, there are only two methods to defeat King. These two methods are either fighting or surviving all of King's attacks for 15 turns. Fighting can end the battle faster if the party's attack damage is strong enough. However, this does not affect the post-battle sequence aside from a minor textual difference regarding how the battle ended.
- How dare you come here, Lightners...?
- You, that left us in the shadows, stripped of meaning...
- You DARE return to torment us once again?
- Begone! We have found fresh purpose.
- For the KNIGHT has appeared.
- The KNIGHT that pulls the Fountains from the Earth.
- Holy Fountains, whose shadows are creating a new world... OUR world.
- Hahaha... Do you see now our NEW purpose...?
- Soon, this world shall be blanketed in darkness... And DARKNERS shall RULE it!
- Then, you may see what it is like to live in DESPAIR!
- Now, enough talk! Fall before the chain of justice!
- ... ha, you're quite strong, aren't you!?
- If I keep fighting you like this, then...
- It seems... that...
- My KNIGHT... I shall not fail you...
- Silence, Lightbringer! Your very existence goes against our own... By the Knight's will, I shall shatter your heart to pieces! [Talk as Kris]
- If I perish, so be it! Show my son the monster you REALLY are! [Talk as Susie]
- Such simple-minded platitudes... A shame you will not live to realize your naivety. Now, perish with the pathetic LIGHTNERS you worship! [Talk as Ralsei]
- King blocked the way! [Encounter]
- Abandoned by the Lightners, his heart became cracked with hatred. He cannot be reasoned with, but don't give up...! [Check]
- Darkness pours from the fountain. [Neutral]
- KING's mouths gave a berserk smile. [Neutral]
- The battlefield is rumbling. [Neutral]
- KING's mouths babble indecipherably. [Neutral]
- KING's cape flutters weakly. [Low HP]
- You tried to reason with the King...
- [King] Silence, lightbringer! Your very existence goes against our own... By the Knight's will, I shall shatter your heart to pieces!
- Your will is changing... TALK became COURAGE! [Talk as Kris]
- Susie tried to reason with the King...
- [Susie] Arright, listen up. Lancer's my friend. So if we can get by without hurting you, then...
- [King] If I perish, so be it! Show my son the monster you REALLY are!
- [Susie] ... Arright, you wanna see what I can do, huh?
- Susie's will is changing... TALK became RED BUSTER! [Talk as Susie]
- Ralsei tried to reason with the King...
- [Ralsei] You might not realize it, but... This is a world where we don't have to fight. I know if we try, we can all find another way...
- [King] Such simple-minded platitudes... A shame you will not realize your naivety. Now, perish with the pathetic LIGHTNERs you worship!
- [Ralsei] Sorry, my friends and I aren't going anywhere!
- Ralsei's will is changing... TALK became DUAL HEAL! [Talk as Ralsei]
After returning to Castle Town at the end of Chapter 2 (if all Darkners from Cyber World are recruited), an interaction between King and Queen occurs in front of the basement jail cell, where King calls Queen "Queenie Beanie" and Queen calls King "Kingy Wingy". These pet names further reinforce possible past relations.
King is Lancer's father. Despite this, they do not appear to have a close relationship, as King spends little time with his son and seems to care very little about his wellbeing, often leaving Rouxls Kaard to look after and even feed Lancer. However, King does seem to care about the public treatment of Lancer, forcing Darkners to take orders from Lancer despite them not liking him.
In addition, speaking to King again in Chapter 2 reveals that his previous threat of throwing Lancer off Card Castle's roof was a bluff he never would have acted on. He also seems genuinely disgusted when the party is convinced he would actually harm his son, confident that Lancer would bounce back up like a "bouncy little pumpkin".
Although not much is known about the Knight themselves, they are responsible for King becoming the absolute monarch of all Darkners in the Card Kingdom. As a result, King holds the Knight in very high esteem, and promises not to fail them at any cost.
King is the ruler of all Card Kingdom Darkners by the time the story takes place. However, everyone seems to either fear King or loathe him, and they are all very eager to have a new ruler replace him.
This is shown during the post-battle outcome where a large crowd of Darkners aid Lancer in overthrowing the tyrant, taking place only if the party hasn't defeated any enemy with violence (excluding Lancer, King, and Jevil).
- King's battle theme, Chaos King, is a remix of the Card Castle music. Both tracks contain elements of Lancer's theme.
- King's laugh is a deeper version of Lancer's.
- In the game files, there exists an unused version of King's battle sprite. The only difference is that King's shade of blue is different from the one used in battle, his legs are more bent, and the end of his spade chain is colored blue instead of gray.
- The King (along with Lancer, Rudinn, Hathy, Clover, Jevil and the uncredited three imprisoned kings) were designed by kanotynes.
- With the exception of Jevil, all of kanotynes's characters were fully designed by March 2012 - 6 years prior to the release of Deltarune.
- During Undertale's 6th anniversary stream, Toby Fox stated that King was being influenced by the Card Kingdom's Dark Fountain, making him more aggressive than he should be as shown through his violent attempts to kill the party in Chapter 1.
- In Chapter 2, King still expresses contempt towards Lightners but appears slightly calmer and less hostile, even showing genuine concern about Lancer's well-being. This greatly contrasts with the previous deranged persona he displayed in Chapter 1.