Heidern is the leader of the Ikari Warriors Team. He marks the official debut in Metal Slug Defense.
Heidern is the commander of the Ikari Warriors, and issues orders to his adopted daughter. Leona and his best soldiers: Clark, Whip, and Ralf. He is also known as the General of the Soldiers of Fortune. After losing his family, Heidern creates the Ikari Warriors, His own Mercenary Unit. He rescues Leona from a raided town, and after seeing her capacities, decides to adopt her as his daughter. He enters many fighting tournaments along with his units, Ralf and Clark; sometime later he recruits Whip. He has a cold personality due to the loss of his family and his eye; He is an experienced strategist, especially when trying to stop an important threat.
- In The King of Fighters series he 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.
- There are rumors about him being the alleged leader of the P.F. Squad, but the rumors haven't been confirmed.
- In Metal Slug Defense, Version 1.44, Heidern, along with Whip, appears now as playable units, as opposed to being character art for the game. Both units cost 300 Medals each.
- In Metal Slug Attack, Heidern is now a playable unit, same with Whip in their respective Extra Ops events as Pre-Acqisition units back then, now available in the Mystery Cranks.
- In The King of Fighters XIV in the Ikari Team Ending, Heidern is been given a briefing of the events from the game, Marco and Fio are spotted in the background.
|Heroes||Marco Rossi | Tarma Roving | Eri Kasamoto | Fio Germi | Trevor Spacey | Nadia Cassel | Ralf Jones | Clark Still | Leona Heidern | Walter Ryan | Tyra Elson | Roberto Nicola | Nathalie Neo | Alisa Stewart | Gimlet | Red Eye | Tequilla|
|Support||Hyakutaro | Rumi Aikawa | Madoka Aikawa | Utan | Issenman Tarou | Eris|
|Villains||Donald Morden | Allen O'Neil | Abul Abbas | Rootmars | Amadeus | Evil Spirit Incarnate | Invader Queen | Allen Jr. | Oguma | Macba | Hilde Garn | Unknown Alien|
|Instructors||Sophia | Margaret | Lilly | Mary | Cynthia|
|NPC||POWs | Parker | Satiko Suzuki | Scott Amundsen Jr. | Miner | Genie of Lamp | Orca | President | Sailor | Rebel NCO|
|Cameos||KOF Team | Battle Cats|
|Unused||Achilles | Tabomba | Ptolemaios|
|MSA Newcomers||Scotia Amundsen | Pharaoh | Red Goblin | El Dorado | Professor | Dragunov | MS-Alice | Abigail | Vatn | Yoshino | Odette | Beatriz | Caroline|