Laharl is the son of King Krichevskoy, ruler of the Netherworld. However, after awakening from a two year slumber, he discovers that his father is dead and almost all of his vassals are gone - most of them are, in fact, trying to take Laharl's place, rather than trying to serve him. As the rightful heir to the throne, Laharl sets out to take the throne by force with his vassal Etna's help, and proclaim himself as the true Overlord of the Netherworld .
He begins by crashing the house of a nearby demon Vyers, "the Dark Adonis", defeating the newly christened "Mid Boss" as the first stepping stone on the path to the throne - a path to be built of his defeated foes. However, his plans are interrupted by the appearance of the angel trainee Flonne, sent from Celestia to assassinate (the late) King Krichevskoy. Chasing the would-be assassin, he eventually manages to corner and defeat her. Laharl then informs her about her target's death, leading Flonne to join his party to study demon nature and threatens that if in need she will switch her target.
Flonne is at first discouraged by his evil behaviour: crashing another demon's house, pillaging it, and then preparing to kill the house's owner, Hoggmeiser. However, Laharl chooses to spare Hoggmeiser when his son, Porkmeiser appears to defend him, leading Flonne to believe that his heart is indeed capable of love. When Vulcanus steals Flonne's pendant, he is enticed by Flonne's promise of "something good" to go and find it. The group finally track it down to Vyers and defeat him once again, recovering the pendant. At this time, Laharl is relieved to find that the pendant burns him, meaning that his heart is wicked.
Even after Laharl is crowned the new Overlord half way through the game, he is still referred to as "Prince" by Etna and all those who still remain in the Overlord's Castle, probably out of habit (although there are hints that several of Laharl's vassals do not see him as worthy enough to replace his father as Overlord.).
It is also shown that Laharl has incredible power within him that he unleashed only when the Seraph had turned Flonne into a flower. It could be that his true power is being held back by his human-half, and only releases the power when he's feeling incredible rage.
In general, the accepted ending is the good ending, in which Laharl spares Lamington's life and is stopped by Mid Boss before he sacrifices himself, allowing him to see Flonne become a Fallen Angel.
In the last episode of the anime, however, Laharl gives the title of Overlord to Etna, then he sacrifices himself in an attempt to revive Flonne. This ending is similar to the normal ending of the game, except that in the game Laharl succeeds in killing Lamington, who would've brought Flonne back to life had he been spared. In the last scenes of the final anime episode it is shown that he has become a Prinny, possessing all the powers he had before when he darkens the sky and very unwilling to work like a regular prinny since he is found in a sun lounger.
The events as written below are non-canon
In the alternate reality Etna Mode in the PSP/DS version, Etna kills Laharl as he wakes up by accident. While playing this mode, the player will not have access to Laharl. In order to prevent suspicion from Maderas, Etna places fake antennas on a Prinny and passes it off as Laharl. By the end of Etna Mode, Laharl is actually revealed to be alive. The shot that supposedly killed him only knocked him out, and he is found by Etna in Stellar Graveyard.
Disgaea 2: Cursed Memories, Dark Hero DaysEdit
Laharl first appears in Disgaea 2 after he learns that Etna has defeated Overlord Zenon, and goes after her to force her to come back to his castle, having had nothing to eat but canned tuna because she took the Prinnies with her. He encounters the party in episode 11 and defeats them easily. However, Rozalin stubbornly stands against him, causing Laharl to break the seal on True Zenon out of curiosity. True Zenon proves far too powerful for Laharl, who quickly runs away (though it should be noted that Laharl didn't even seem injured after the fight, just frustrated that he wasn't able to overcome her). He later returns and tries to make himself the main character of Disgaea 2, blaming not being the main character for his defeat. It's revealed that the reason Etna left was because Laharl stole her rare pudding. He is playable after completing the optional missions "I want to fight an Overlord!" and "Summon Laharl!". When completing the final mission, Laharl joins after tasting Hanako's cooking since he can't make her his chef. In the good ending, Etna goes back to serving him and Hanako joins her.
Disgaea 3: Absence of Justice, Absence of DetentionEdit
Laharl appears before Mao, who Laharl assumes to be the legendary Overlord who stole his height(Claiming to be 6'6). Mao, however, believes that Laharl is the legendary Overlord and the two fight. When the battle ends, Mao and Laharl appear to be evenly matched until Almaz makes them realize that neither of them are the legendary Overlord. Laharl, along with Etna and Flonne, joins the party and reveals to Mao that the legendary Overlord they have all been looking for is Baal.
In an alternate battle, Laharl suddenly appears before Mao alongside Etna and Flonne, claiming to be Mao's father. Mao doesn't believe him at all, but later begins to call Laharl his old man after defeating him. However, it turns out that this was all an attempt to steal the lead role and he reveals to Mao that he is actually another Overlord after the battle. The game ends after this.
Disgaea 4: A Promise UnforgottenEdit
Laharl is a boss in the game's post game and is unlocked after being defeated, much like in previous Disgaea games. He tries to take over the presidency and the Netherworld again, as well as the spot of main character, but loses to Valvatorez and the gang, upon which he becomes impressed by their power and turns them all into his vassals. Fenrich expresses disapproval of this, as well as the idea of Laharl hijacking the "main character" role, but Valvatorez shrugs it off as he is more determined in finding the cause of the abnormal phenomenon in the Netherworld. There is DLC specifically for him, in which Laharl attempts to boost his popularity by copying Archangel Flonne's giant mecha, creating his own Gundam-like pirate ship called Laharl Kaiser V.
Laharl overhears Prinny talking about a secret and easily learns that Etna ordered a limited-edition pudding from the Sea of Gehenna. Wanting to steal and eat the pudding for himself, he orders the Prinnies to look for the pudding. After the main Prinny finds TickTock and is rendered unconcious, Laharl enters the room. Furious, he orders the Prinny to find the pudding. Unfortunately, the Prinny trips and falls through a window. He decides not to trust the Prinnies and goes looking for the pudding himself.
Prinny: Can I Really Be A Hero?Edit
Laharl appears as an optional boss in the game. In the game, he is in his Prinny form (from the Normal Ending) complete with his scarf, red eyes and antennas. During the battle, he attacks using his Prinny Knives, a smaller Overlord's Wrath that hits twice and using an alternate version of his Meteor Impact attack which first he uses a Gear Metal YAY, then an oversized bomb and a table.
Laharl can be defeated in 2 ways: By depleting his HP to zero or by lifting him up and throwing him (since he's a Prinny, he explodes when thrown). It is revealed that he was forced to work for Etna after returning to the Netherworld and that out of frustration from being overworked, stole Etna's Sea Of Gehenna Pudding and ran off, causing the game's events. Etna comes in and says that she was only overworking him because she wants him to be able to reincarnate back into his old body. Also, The Hero Prinny states that he heard Laharl's laugh somewhere before but can't put his finger on it, so thus he doesn't realize that he beat Laharl.
Prinny 2: Dawn of Operation Panties, Dood!Edit
In the sequel to the original "Prinny: Can I Really Be the Hero?", Laharl is an additional playable character. His abilities are more powerful then the Hero Prinny's abilities and he throws fireballs instead of attack with Knives.
In Makai Kingdom, Laharl is brought before Overlord Zetta after Etna and Flonne were defeated by him, and tries to show Zetta that he is the superior Overlord in an extra boss battle. He can be recruited after defeating Flonne and Etna by writing the wish "I wish to fight the Overlord of another Game!" Upon recruitment, he is an ATK-based character good with Swords, Spears, Axes, and Beam Swords. If Laharl is the leader character when you defeat Overlord Baal while he's in Zetta's body, Laharl destroys Zetta's body to prevent Baal from escaping which causes the credits to roll. However after the credits are done, the player is greeted with the Game Over screen, sending the player back to their last save point.
Phantom Brave, We Meet Again, The Hermuda TriangleEdit
Laharl is also present as a boss in Phantom Brave. He is trapped in a Bottlemail and after meeting the main characters Ash and Marona, he constantly tries to make them his vassals by defeating them.
After beating him 3 separate times, Ash and Marona fake a loss so that Laharl will stop fighting them, and Laharl gives them his Phantom Double, adding Laharl as a playable character. In battle, he specializes in ATK-based skills, but can also dabble in INT-based skills as well.
Soul Nomad and the World EatersEdit
He also makes a brief cameo appearance in Soul Nomad. In the demon path, should the main character choose to call himself the Overlord over the Devourlord ("Eh, Overlord is fine I guess."), Laharl scolds him/her for taking such a title lightly. Revya and Gig, however, ignore Laharl and the story continues from there.
Zettai Hero Project: Unlosing Ranger VS. Darkdeath EvilmanEdit
It has been revealed that the Costume System of the new game Unlosing Ranger Vs. Darkdeath Evilman will allow the Unlosing Ranger to don a Laharl costume, allowing one to, in a sense, play as Laharl. In one of the possible endings, Laharl appears and proclaims that he is a powerful Overlord. After looking at the main character, he assumes the hero thinks he is short and as a result, burns him to death and burns the whole planet.
Laharl is incredibly arrogant as well as snarky and always tries to prove that he is the strongest demon in the Netherworld. He is, however, extremely powerful for his appearance, which, despite his age, is still that of a small human child (his large hair antennae and billowing scarf are meant to mask this fact). However, he has a weakness towards (as in, he literally gets hurt by) optimistic sayings (especially anything concerning the word 'love') and women with sexy bodies. Maderas took advantage of both weaknesses in both the game and the anime by having pretty girls say optimistic things (succubi in the game and miscellaneous pretty demon girls in the anime). He claims that Flonne and Etna don't bother him since they're flat-chested, something which they obviously take as an insult. He appears to have gotten over his aversion in his later appearances, as he isn't bothered by Rozalin's revealing outfit (Although a conversation with Machiko in Disgaea 3 after being recruited shows he's still highly nervous around them). Although Laharl considers himself evil, he never does anything that may be considered truly amoral. He only briefly considers doing anything to the Earth, and the only things he can think of are making it rain pepper and giving kids an addicting video game. Laharl also loves to laugh evilly, believing it is an important part of being the Overlord. Even when towards the end of the first game when Laharl has clearly turned good, he still continues acting like he's evil, except for when Lammington turns Flonne into a flower. At that he point he displays outright hate for the Seraph, believing that he turned on Flonne after she believed in him. This is, and in the normal ending where Laharl sacrifices his life to revive Flonne, are the only times he admits to caring about her, any other time he denies doing so. It is strongly implied that he harbors romantic feelings for her because the only way to cast the revival spell that takes the user's life is if the user has love for the person he/she revives, similar to how Laharl's mother took her own life to cure Laharl's deadly disease. This is the reason Laharl rejects love and thinks love is useless because it was the cause of his mother's sacrifice.
In Laharl's future appearances, he maintains his ego and view that he is evil, and displays outrage whenever he isn't the main character, and attempts to take the role from whoever it happens to be at the time. His obsession with this is perhaps best shown when he appears in Disgaea 3, where he accuses Mao of being the "Legendary Overlord" that stole from him, but reveals after fighting him that he knew it was really Baal and only accused him just so he could increase his screen time.
In Disgaea 4, Laharl again appears in the post-game, wanting to become the new protagonist of the story and take over the Presidency from the challengers aiming to get at it, after Axel, Raspberyl, and others try to take it. He loses against Valvatorez and his party, and joins the party, supposedly to increase the time he spends on-screen.
Laharl is the usual "Hard-Hitting Warrior" character. His attack stat and aptitude are both high to suit this. His weapon of choice is a sword, making Laharl flexible and easy to level due to the Sword Skill "Winged Slayer" (or "Slayer's Descent" in the third Disgaea game). His Unique Special is Blazing Knuckle where he will jump up and punch the ground hitting his two sides, his back and his front. Overlord's Wrath has a cross hit pattern where he will launch multiple balls of light and crush it to the ground. Meteor Impact will take you to another dimension and Laharl will jump on a meteor hitting his four sides plus two or more squares. Laharl can wield any melee weapon with ease however, as he has a Mastery of "A" in every weapon except for Guns and Staves.
- Laharl, Etna, and Flonne are the only Disgaea main characters to appeare in every Disgaea game.