Heidern (ハイデルン, Haiderun) is a character in The King of Fighters series who debuted as a playable character in The King of Fighters '94 in the Brazil Team (later known as the Ikari Team), along with Ralf Jones and Clark Still.
Heidern is the commander of the Ikari Warriors, and issues orders to his adopted daughter Leona and his best soldiers: Clark Still, Whip, and Ralf Jones. He is also known as the General of the Soldiers of Fortune.
He was conceptualized to be a "cold-blooded killing machine", but his designer grew attached to Heidern and gave him a tragic past.   His namesake is a character from the anime, Space Battleship Yamato. His eccentric and uncommon fighting style surprised some of the staff, and they humorously wondered if they should add a supernatural quality in his character history. Toyohisa Tanabe states that Heidern was added to be the "particularly strong" character at the time of his debut.
In regards to his tragic past, the developer asked the planner what Rugal thinks of Heidern, as Heidern clearly despises him; he responded:
“Well, Heidern basically was just in the wrong place at the wrong time when he crossed paths with Rugal… and Rugal just swatted him like a fly, kicked him aside like a rock in the road.” 
Eight years prior to The King of Fighters '94 tournament, a 34 year old Heidern was just promoted to his current rank for his exceptional proficiency in martial arts and strategy. The event took place at a top-secret base in Brazil and his wife and daughter were present for the ceremony. Rugal Bernstein, who caught wind of Heidern's high marks, stormed the base when he was away and killed fifty secret service officers on his arrival. When Heidern hurried back from his duties, Rugal deprived him of his right eye and deemed him unfit to be a part of his collection. Instead, he murdered Heidern's wife and child. Disgraced and alone, he developed his own fighting style and mercenary unit, the Ikari Warriors. Since then, he pursued Rugal to avenge his loved ones' deaths. 
Sometime before the King of Fighters tournaments, he found Leona as the last survivor of a destroyed village. The girl was amnesiac and Heidern adopted her to care for her. He originally forbid her to partake in any training yet became lenient due to her inclinations on the matter. His refusal to give her a formal rank is his way of protecting her from some of the dangers on the battlefield. Beginning in The King of Fighters '96, he assigns Leona to take his place in the tournaments while he issues orders from the sidelines. 
He continues to play a major part in one of the series' story arcs, the NESTS Saga, since the Ikari Warriors are trying to destroy the NESTS group. Heidern and his group found Krizalid's corpse and brought it back to their base, however it would soon be taken by Zero not long after. At one point, his own group was infiltrated by one agent of NESTS who stole the identity of one of his ally and attempted to sabotage their operations. Heidern killed him once he saw an opening.
He participates in The King of Fighters 2001 tournament alongside Ralf, Clark and Leona. They advance through the tournament, but is defeated by the Hero Team with Heidern losing to the leader. Heidern reveals that his reason for entering wasn't to win, instead it was to locate the leader of NESTS using the KOF tournament as a distraction. In the teams ending, Heidern announces to his group that the NESTS case is closed.
Months before The King of Fighters 2003 tournament, Heidern sent his men to investigate the flying vessel known as Sky-Noah.  When Leona experiences the Riot of the Blood after the 2003 tournament, he decides to pull her out of the following one and stay by her side while she recovers. After hearing Ralf and Clark's personal assessment of Leona, he lets his adopted daughter enter the tournament once more. In the end of KOF XI, the Ikari Team managed to secure Magaki's corpse and intended to analyse it, but the cruise they were on got invaded by Shroom and Rimello. The duo took Magaki's corpse, and Shroom also stole Heidern's eye patch and began to wear it as an insult and proof of his ability.
Heidern orders the team to investigate whatever role Those from the Past and Rose Bernstein have in the KoF XIII tournament. He also updates Seth, Vanessa, Ramon and Blue Mary on the current situation and tells the agents to disembark on the navel port so they could infiltrate the stadium and find out what Ash and the clan are planning. He puts Seth in charge of the matters on the side.
Heidern hands the invitation to the Ikari Team and confirms that he's already done a background check on the tournaments host. He informs the team on the recent reports regarding the distortions in spacetime, along with NESTS activity increasing during the same time period. He tells them to infiltrate as usual. 
After receiving the information Maxima provided Heidern dubs the entity as Verse, he tells everyone in the room to continue their investigation. 36 hours after the tournaments conclusion, Heidern confirms that there's bodies that were resurrected and has already commenced a 24 hour surveillance. After the meeting he tells Leona that Gaidel's resurrection has not been confirmed, Leona responds that she's not concerned.
Very calm and silent, Heidern's personality was built because of the trauma of losing his eye and his family to Rugal. Although he hides his emotions through a veil of professionalism, he cares deeply for all of his subordinates, especially for Leona.
Heidern is very strategic, especially when trying to stop a major threat, and has used his group Ikari Warriors to deal with such threats appropriately; he has been known to enlist mercenaries and free agents too.
Outside his sphere of acquaintances, he can be either confrontational, haughty or demanding on the skills of whom he comes up with, and doesn't mince words to call out what he perceives as inferiority. He's quick to praise competence and effort in fighting, however. Whenever he faces anyone he has encountered before (ie. acquaintances, allies, employees, subordinates or colleagues) in combat, he is rather respectful and recognizes their will to be strong.
- Slashing Hands - Heidern's hands can cut and pierce as if they were knives.
- Cutting Aura - Aside of his slashing hands power, Heidern can create a cutting aura around his arms.
- Cutting Projectile - Heidern can send a cutting/piercing projectile flying with his hands.
- Absorb Life - By piercing his hands in his enemy's body, Heidern can absorb his or her life-energy and refill his own.
- Tactical Administration - Being a leader of a military-like mercenary group, he has held and dealt with several personalities, including his own band of soldiers, the Ikari Warriors. Apart from Ralf, Clark and Whip, he hires mercenaries and free agents to expedite work, as he is seen assigning missions to Vanessa, Seth, Ramon, Blue Mary, and many others as well.
- Tactical Planning - Seen in KOF99, KOF2000 and KOFXIII, Heidern has been the brains behind coordinated actions against many of the series' organized antagonists, with significant results.
Heidern employs his self-made fighting style. Said fighting style is a striking martial art with emphasis on his cutting hand strikes. He is the master of his own brutal self-made martial art, involving cutting with the use of bladed gloves, which seem to conceal explosives and a form of energy generator (used for his signature attack, Storm Bringer, which is a reference to the famous Stormbringer sword).
In KOF 2001, he has been turned into a command-based character instead of his usual charge-based moves. This was corrected in his appearance in KOF 2002 UM, where he reverts to his charge-based commands.
- Jungle Bouncer - The King of Fighters '94
- Desert Requiem - The King of Fighters '95, The King of Fighters '98: Ultimate Match (when teamed with Ralf and Clark)
- In Spite of One's Age - The King of Fighters '98
- My Whip - The King of Fighters 2001
- In Spite of One’s Age ~Ver.Immortal~ - The King of Fighters 2002 Unlimited Match
- Desert Requiem ~KOF XIV Ver.~ - The King of Fighters XIV
- Toshimitsu Arai - The King of Fighters '94~The King of Fighters 2002: Unlimited Match
- Haruo Yamagishi - The King of Fighters World~present
- Ikari III: The Rescue - in the NES version intro
- The King of Fighters '94
- The King of Fighters '95
- The King of Fighters '98
- The King of Fighters 2000 - as a PS2 Maniac Striker for Whip
- The King of Fighters 2001
- The King of Fighters '94: Rebout
- The King of Fighters '98: Unlimited Match
- The King of Fighters 2002: Unlimited Match
- The King of Fighters XIV - DLC character
- Days of Memories (first title) - NPC
- Athena On Stage - band member
- The King of Fighters '98 Ultimate Match Online
- Metal Slug Defense
- Metal Slug Attack
- The King of Fighters: Destiny
- The King of Fighters: World - NPC
- The King of Fighters: All Star
- The King of Fighters M《格鬥天王M》
- The King of Fighters '96 - in Chizuru's stage
- The King of Fighters '99 - during in-game scenarios
- The King of Fighters 2000 - during in-game scenarios
- The King of Fighters 2002 - televised in the Mexico and Italy stages and in ending credits
- The King of Fighters XI - in the Ikari Warriors Team, Agents Team, and K' Team's endings
- The King of Fighters XII - passing mention during Leona's profile story
- The King of Fighters XIII - talks to Ralf and Clark during the Ikari story, in the Sky Noah stage and in the mixed team's ending
- The King of Fighters XIV - in the Ikari Warriors Team and K' Team endings
- KOF: Maximum Impact 2 - Leona Normal Outfit-Variation G
- Capcom vs. SNK 2 - background cameo
- SNK Gals' Fighters - in one of Leona's attacks
- The King of Fighters (pachinko)
- The King of Fighters 2
- The King of Fighters: Battle de Paradise
- Nariyuki Quest
- SNK Heroines: Tag Team Frenzy - in Leona's ending; also mentioned in Leona's prologue with Love
- Heidern has also used the codename Bechstein in the past. Adelheid also gives him the nickname Heidi, which is a reference to the German novel character.
- In the Ikari Team's backstory for XI, Ralf mentions that his and Clarks relation with Heidern is best represented by the white magnolia flower from the funeral they attended. In flower language, it means deep unspoken trust. 
- In KOF XIV, Heidern retains a unique function to increase the damage of his next Stormbringer attack whenever he whiffs his Moon Slasher, which is a nod to an infamous one-hit-kill bug that functions the same way in the original KOF '94. More can be seen in detail here, as the easter egg in the former game has been re-balanced to prevent it from being game-breaking.
- ↑ THE KING OF FIGHTERS XIV website from the DLC character page.
- ↑ 2.0 2.1 The King of Fighters ’94 – Developer Interview originally featured in the “All About KOF’94” mook
- ↑ Official character profile from KOF anniversary website.
- ↑ The King of Fighters '94: Ikari Team Story from KOF anniversary website.
- ↑ The King of Fighters '96: New Ikari Team Story from KOF anniversary website.
- ↑ The King of Fighters 2003: Ikari Team Story from KOF anniversary website.
- ↑ Ikari Team Prologue from THE KING OF FIGHTERS XIV website.
- ↑ http://kofaniv.snk-corp.co.jp/english/history/kofxi_story/index.php?num=ikari The King of Fighters XI: Ikari Team Story] from KOF anniversary website.