Clayman

Kleiman (クレイマン), known as Marionette Master (人形備偏師), was a Demon Lord, in the era of the Ten Great Demon Lords. Being a Demon Lord Seed, he lacked some power in comparison to older generations of Demon Lords. He was considered a ghastly man, infamous for his acts of manipulating his subordinates and others like dolls.

Appearance
Kleiman had the appearance of a wealthy noble. He had a slim, oblong head topped with pale lavender hair; a face with a sharp chin and defined jawlines, and a pair of pointed ears on either side and thin eyebrows. He sported a slender figure, and his eyes with red irises exuded intelligence even as they suggested he was rather high-strung.

Kleiman wore expensive and elegant clothes sharing an overall white motif – a long white tailcoat, grey vest, white shirt, slim white trousers and white shoes, alongside black bow-tie. In his inner pocket of his tailcoat, he kept a gold-plated pocket watch with an engraving on its lid, the chain of which could be seen.

In his combat form, his skin was darker, his entire figure changed - four more prosthetic arms and a tail emerged. In place of his elegant tuxedo was a wrought-iron breastplate, codpiece, and spiked pauldrons and armor for his legs. When he donned his mask and acted as the "Crazed Clown," he seemed more like a mad beast instead.

Personality
Kleiman was a cunning and manipulative Demon Lord, preferring to manipulate things in the background rather than get into conflict himself. He specialized in intelligence gathering with the use of his ability in order to perfect his scheme to obtain more power.

Kleiman treated his subordinates and those he considered below him very poorly, and would throw away those who were no longer useful to him and force others to submit using his unique skill, even having the force of will to make almost anyone follow his orders.

He was also very stubborn and prideful, refusing to admit when he made errors that put evidence about his involvement in many of his plots and almost every Demon Lord was already aware of his conspiracy to become a True Demon Lord. Kleiman also never liked to state his opinion of his fellow demon lords publicly. This is shown clearly when Milim was "mind controlled" by his artifact, and when he believed she truly was under his control, only then did he start to insult her and gave his personal opinion of Milim, showing that Kleiman was also a coward.

As seen in his actions and noted by his creator and comrades, Kleiman was noted to be quite arrogant and overconfident in his abilities when things seemed like they were going according to his plan, as seen where he made several tactical errors during his plots against Rimuru and Tempest, such as assuming he had successfully mind controlled Milim despite her being infamous for being uncontrollable, assumed that Frey was his ally loyal to him alone and believed that he was powerful enough to overpower Rimuru and Shion due his supposed "control" over Milim. This personality trait was noted by both Kagali and Laplace to be one of his most prevailing traits despite their warnings for him to adjust it.

However, for all of his manipulative and power-hungry tendencies, Kleiman, much like his creator was very gentle and considerate towards those who he considered his friends and comrades such as the Moderate Harlequin Alliance. He also respected and followed his superior's order with absolute loyalty. This is seen during his final moments, when he refused to divulge any information on his superiors or his comrades during his final stand against Rimuru despite being threatened with the complete and utter eradication of his soul, with Raphael acknowledging and calculating that it would be extremely difficult to get Kleiman to talk.

Background
Kleiman was created by Kagali as a Deathman many years ago to be part of the Moderate Harlequin Alliance, known as The Crazy Pierrot. Kazalim himself personally designed Kleiman to be a tactical commander and a schemer, similar to himself and created him for the expressed purpose of turning him into a Demon Lord.

300 years ago, he became one of the Ten Great Demon Lords with Kazalim's help, in order to increase his own influence in the Demon Lord Council. The moment he became a Demon Lord, he began hunting down Majin and monsters to steal their hearts (literally). Making them swear loyalty to him, he inscribed a curse onto their hearts, making them his eternal servants. That's how Five Fingers was born, containing cursed pet Ninehead, Immortal King Adalman, top lieutenant Yamza, witch Mjurran, spy and intelligence collector harpy Pirone.

Eventually his master was killed and replaced by Leon Cromwell on the Demon Lord Council. With Kazalim gone, Kleiman had to take over his domain, the Puppet Nation Jistav and all of his remaining forces. Kleiman hadn't received any words from him for a long time, but still considered himself to be the subordinate of Kazalim. He still continued working on his goals, while still waiting for his master's return.

Kleiman wished to get rid of Leon in retaliation for Kazalim's demise. In order to achieve this, he hired many mercenaries, however, they all failed to carry out the task, instead getting slain by Leon's entourage each time.

Kleiman, alongside Carrion and Frey, were considered the new generation of Demon Lords, so they would work together, in order to expand and increase their influence and power base. Their goal, also was to bring the gap of power between them and older generation Demon Lords. Being one of the active Demon Lords, his name was greatly known among humanity and other nations. Kleiman was close enough to taking over the entire world, and it was all through his trading relationships, which, generally most Demon Lords won't do. He was the wealthiest among all the Demon Lords, and his wealth did not only come from trading but from the artifacts that were buried beneath the ruins of Amrita which ultimately made him a powerful foe politically and economically. Damrada states that Demon Lord Kleiman was a valuable trading asset for the Eastern Empire.

At some point, he met a mysterious patron who offered Kazalim's resurrection in exchange of the Moderate Harlequin Alliance's help in taking over the world. Kleiman agreed to this request.

Trivia

 * The "Klei" in Kleiman means string or wire. Thus his name can be inferred to mean Stringman.
 * To keep his mind sharp on a daily basis, he regularly played chess.
 * During the era of the Ten Great Demon Lords, Kleiman was effectively the most wealthiest Demon Lord among his peers, with a large amount of wealth earned from trading with the Eastern Empire and several other influential nations and parties, while the rest came from selling several artifacts that once belonged to Kagali's old city Amrita.
 * Kagali states that she had to sacrifice much of his raw power during his creation in exchange for more intellectual ability and intelligence, thus explaining why he is weaker than the average Demon Lord Seed.
 * Kleiman was the only one among his fellow Jesters who couldn't meet his master Demon Lord Kazalim personally after he assumed the form of Kagali, Yuuki's secretary.
 * There were obvious hints that Kleiman was being brainwashed. The first hint was that he was exposing himself as the mastermind behind Eurazania's invasion as well as unknowingly revealing his scheme to become a True Demon Lord. The second hint was that he refused to wait as ordered by his master Kazalim, which was something he generally wouldn't do as he'd always follow his orders to the letter.
 * Even if Kleiman did survive his battle against Rimuru by fleeing the Walpurgis through the use of his Giant Magic Missile or fake his death and flee the Banquet by his Astral Body, he would most likely lose his title as a Demon Lord either way.
 * Much like his creator Kazalim, Kleiman lost his Demon Lord Council's seat and his life due to a newcomer Demon Lord.
 * Kleiman's initial appearance greatly varies in the anime and the manga.
 * It is highly implied that the only reason Kleiman held his Demon Lord's seat and caught up to the other Demon Lords despite being the weakest was due to his scheming capabilities.
 * Excluding his fellow peers (till his scheme was revealed), Kleiman was disliked by majority of the Demon Lords, for either being a newcomer and a schemer who aimed too high for his abilities, or for his treatment of his subordinates, or the fact that he is very weak.
 * Kleiman achieved a certain proficiency over pastries, especially in the production of confectionery products such as scones, biscuits, cakes and pies. His homemade products were scrumptious, even more so when paired with aromatics teas grown and harvested on Jistav's local fields.
 * In order to utilize and perfect his pastry skills, Kleiman regularly announced and invoked tea parties with fellow Demon Lords, not forgetting to elicit new facts and information from the guests.
 * Kleiman was one of the few Demon Lords that was liked and recognized by Guy Crimson's maid - Rain. She appreciated his coordination skills and respected his courage to call himself a Demon Lord, even when he was weaker then herself. Rain liked the convenience he offered her, as after prodding him a little, he would handle the tasks which she found troublesome. He was an overall useful person to her. Rain greatly regrets his loss, reasoning that he chose the wrong person to oppose.
 * Considering Guy Crimson being the mediator of the world, it is highly possible that he would oppose Kleiman's plans to conquer the world, which was already in place thanks to his trading relationships.
 * Despite being killed during the events of The Octagram Soars Brightly, his name was still often brought up in later volumes as a benchmark to describe the strength/energy amount of new characters. The author jokingly mentioned that Kleiman effectively became a "combat strength measurement unit."
 * His Japanese VA in anime,, is well known for playing twisted and manipulative evil masterminds, such as Dio Brando in JoJo's Bizarre Adventure and Sugou Nobuyuki in Sword Art Online. Needless to say, this is very fitting for Kleiman's character.