Heidern (ハイデルン) is a character in the Ikari Warriors series. While he made his brief debut in the intro of Ikari III: The Rescue, his playable debut began in The King of Fighters series in The King of Fighters '94, where he lead 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: Ralf Jones, Clark Still and Whip. His official nickname is "General of the Soldiers of Fortune" (フォーチュンソルジャーズジェネラル) and, in KOF XV, is "Hard-Boiled Assassin" (
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." 
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 their life-energy and refill his own.
- Explosions: Heidern can create explosions, through his own gloves. His adopted daughter also learns this ability from him as well.
- Tactical Administration and Management - Being a leader of a military-like mercenary group, he has managed 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 KOF '99, KOF 2000 and KOF XIII, Heidern has been the brains behind coordinated actions against many of the series' organized antagonists, with significant results.
- Fishing - One of Heidern's hobbies that most likely ties in with his survival skills and recreation.
- Game Hunting - Heidern's other forte most likely helps him keep his senses sharp while providing a pastime and recreation.
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.
- Jungle Bouncer - The King of Fighters '94
- Desert Requiem - The King of Fighters '95, '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
- Time for revolution It's our generation - The King of Fighters XV
- Toshimitsu Arai - The King of Fighters '94~2002 Unlimited Match, Metal Slug Defense & Attack (recycled audio)
- Haruo Yamagishi - The King of Fighters: World~present
- 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 Clark's 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 '94, Heidern had a bug where he could increase the damage of his next Storm Bringer or Final Bringer attack whenever he whiffs his Moon Slasher, often leading to a one-hit-kill. Particularly in KOFXIV, it has been re-implemented this time as a slight easter egg, no longer game-breaking and now in a balanced manner as the damage increase is no longer as apparent yet is quite slight-yet-still notable (and also applies to his later Killing Bringer move as well).
- In the Game Boy version of KOF '95, his name is misspelled as 'Jeidern'. However, in the Japanese version, his name is spelt correctly.
- Heidern's "Storm Bringer" attack is named after the famous Stormbringer sword.
- In KOF 2001, he has been turned into a circle motion-based character instead of his usual charge-based moves. This was corrected in his appearance in KOF 2002 UM, where he reverts back to his charge-based commands.
- THE KING OF FIGHTERS XIV website from KOF XIV DLC character page.
- - "The King of Fighters ’94 – Developer Interview". Archived from the original.
- Official character profile from KOF anniversary website.
- The King of Fighters XI: Ikari Team Story from KOF anniversary website.