Heidern was a very spirited soldier in his young times, training very hard and accomplishing his goal of being the best of his class. Participating in several wars as a mercenary, Heidern was feared as a man with hands like claws, and his cutting-edge fingers. Heidern also fell in love with a precious woman named Sandra, and decided to marry her. Not much time later, they had their only daughter, Clara. Heidern was very happy with his family, and after having received the title of commander, he retired to pass more time with his family.

However, there was one last mission assigned to Heidern. He and his unit must investigate a man who has gained a name for himself in the black market, and has become such a powerful man, that he represents a menace to the world governments. He was called Rugal Bernstein. Heidern accepted, conditioning that his family must be safe at all moments. The governments located a security group in front of Heidern's house, so Heidern was free to investigate Rugal. Or so he thought...

Heidern dedicated himself day and night to follow the trace of Rugal. He seemed to pop up everywhere, even in two different continents the same day! Heidern did not know what made Rugal so fast, but he managed to bust some criminal warehouses and other illegal locations properties of Rugal. However, Rugal was nowhere to be found. Amidst the tedium and desperation, Heidern wanted to see his family again. Given permission to do so, Heidern traveled back to his house for a certain period of time. When he came back, he saw the security force totally wiped out, and his family missing, his house trashed. Then, Heidern saw a letter on the table. It was signed by a certain "R" individual. Heidern opened the letter, and it was Rugal! He told Heidern he had his family, and that he should better stop all that foolishness of trying to stop him and play hero. If he declined the investigation, he would free his family again. Heidern slashed the letter to pieces, and now more than ever, was dedicated to trap Rugal.

Sooner than ever, Heidern located Rugal's trail. It seemed he had a personal air carrier called the 'Blacknoah', where he voyaged with an impressive arsenal. Heidern gathered his unit, and took the plane that would take them to the Blacknoah. They landed on the Blacknoah soon after, surprisingly finding no resistance. After penetrating the carrier, Heidern found Rugal ready for battle. Rugal laughed and considered them all to be fools. Before they could do anything, the unit was almost plowed by Rugal's inmense power. Just in a few minutes, Rugal had taken out all of Heidern's unit. Heidern was so shocked he barely noticed how Rugal got closer to him. Heidern, enraged, took Rugal on. But his fury did not allow him to fight well, and Rugal and his huge strength made short work out of him. In a single move, Rugal managed to gouge out Heidern's right eye. Wounded and unable to go on, Rugal prepared to deliver the final blow, but if he had to die, he must at least die in style. Rugal then began to gather huge power, and before he unleashed it, Sandra and Clara appeared to cover Heidern. Heidern shouted for them to stay away, but they did not listen. A blinding light fazed Heidern, and then all became blank.

Heidern woke up in a hospital bed. He was wrapped up in bandages, and his eye covered with a patch. His nearest nurse got closer to him, and Heidern desperately asked her for information on his unit and his family. His unit: Almost all killed, the survivors badly wounded. His family: Dead. Heidern was destroyed. He passed many months in grief and pain, and burned in desires of taking revenge on Rugal. As of destiny would have had it, a little girl appeared sleeping in the jungle near Heidern's house. She was filled with blood, but she had no wounds. Maybe it was other's blood? Heidern felt compassion for the child, and took her home. Once, he noticed the incredible power she had, and he decided to train her personally in martial arts. She said they used to call her Leona, but that's all she reminded of her past. Also having the company of his best mercenaries Ralf and Clark, Heidern's pain was quenched, but his revenge was soon to be realized: he received a personal invitation to the new King of Fighters tournament, which had the new team battle mode. Taking Ralf and Clark with him (since Leona was still too little), Heidern faced the tournament. He didn't reach the finals, but he was relieved when he knew about Rugal's death after his carrier being destroyed. That was, until next year...

Heidern was invited once again to the King of Fighters tournament, and he suspected that something fishy was going on since the invitations were signed by "R". Calling Ralf and Clark back to duty, the trio once again investigated, and indeed, it was Rugal once again! Heidern was ready to end the score with Rugal, but realized it was all up to Kyo and his team. He aided the Hero Team in all he could, and when Rugal was finally destroyed by his own power, Heidern considered it a proper death for a man thirsty of power, and walked away.

After that, Heidern declined all future invitations to the King of Fighters tournament, since Rugal was destroyed, and he had nothing to do with it anymore. So, he sent his best student, Leona, to fight along with Ralf and Clark, the persons he sees as his sons. He especially cares for Leona, not only just because she resembles Clara so much, he also wishes that Leona can finally get over her past, and when she does, Ralf and Clark will be with her. Heidern, after all, is still able to care for other people.

Shortly after the 1997 version of the King of Fighters tournament ends, and with the situation back to normal again, Heidern receives the visit of a young girl. She calls herself Whip, and wants to enter the Ikari Warriors squad. After seeing her impressive skills with a whip, Heidern brings her in, and decides to train her in his own assasination techniques. After two years, Heidern detects some strange anomalies during the King of Fighters 1999 tournament, so he dispatches his best Ikari squad to investigate. And soon, results would jump to sight....

Heidern manages to detect from his command room several images of Kyo Kusanagi around the world. This is a weird success, indeed, and it makes it look like the tournament is nothing more than a set-up. Heidern tries to contact his unit, but fails. Thus, he decides to dispatch several elimination squads to the location of the Kyo clones, and prepare to eliminate them. After that, Heidern directs himself to the main base of the enemy. Upon arriving, he notices the several wounded bodies of his soldiers among the ruins, and one dead body: that of the past host of the competition, Krizalid. Heidern closes the eyes of the deceased man, and asks for any survivors. One soldier noticed two persons evacuate the place before they arrived. Heidern feels the menace is barely starting...and not yet reached the full terror.

After a while upon investigating the NESTS cartel, Krizalid's organization, Heidern finds himself stumped and without a clue. It is then when he is given a helping hand by a fellow mercenary commander Ling. Ling informs Heidern about the most recent location of NESTS: in Southtown. Heidern considers it ironic for the tournament to return to its' origins. Ling also tells Heidern that he will organize the new King of Fighters tournament in the year 2000 in order to get the strongest fighters to do battle against the NESTS agents if they ever appear. Heidern assists to Ling's command room in order to supervise the mission. Their primary objective, aside from destroying NESTS, is to locate K' and Maxima, who also have close ties with the NESTS.

As the winning teams approach Southtown, Heidern senses something going terribly wrong as his soldiers investigate the wrong direction. Ling tells Heidern that he has sent the soldiers to the factory zone in Southtown in order to turn on the elevator and activate the generator in the abandoned factory. Heidern is dumbfounded, but before he can ask anymore questions, he is held at gunpoint by Ling's soldiers! It turns out to be that Ling is not really Ling, but Zero, a NESTS officer who had created a clone of himself (in the form of Ling) in order to gain the trust of the participating fighters and the world leaders, fooling them into believing that he realy had a clue in order to find and destroy NESTS. Heidern then knows about the sinister plans of Zero, involving using the energy of the warriors in order to activate the Zero Cannon, and being able to destroy any designated point on earth! Heidern is then knocked out cold by Zero's agents, but is later waked up by his elite mecenaries: Ralf, Leona, and Clark. The whole Ikari Warrior squad decides to escape before the Zero Cannon destroys Southtown completely...all, except one.

Heidern realizes with panic that Whip is missing. Heidern desperately calls Whip via radio, calling Whip by her real name, which only he knew up until then: Muchiko. However, Whip does not respond to Heidern's demands, and the commander of the Ikari Warriors is forced to escape before the Zero Cannon vanquishes Southtown into dust. After that, Heidern finds a video in Whip's quarters directed to Heidern and his closest followers. The video contains a warm goodbye by Whip, and a reminder to Heidern that her name is not Muchiko, but Whip. Heidern gives a sad smile, and hopes that, wherever she is, Whip might find happiness.

After scouting the ruins of Southtown, Heidern realizes that NESTS has abandoned Southtown without leaving a trace. So, he begins to gather his forces in order to attack and arrest all NESTS officers in several locations around the world. Heidern sends his best men to do the job, but unfortuantely, they have no success at all. It is then when Whip sends a letter to her former commander, telling him that NESTS is about to make their move, and they're planning to use the King of Fighters tournament was their new arena! Heidern summons his best officers to his quarters: Leona, Ralf, and Clark. Heidern thinks it's pretty obvious that NESTS is planning something big, entering the tournament when they had just destroyed a whole city. And since the Ikari Warriors were short one member ever since Whip leaved, Heidern thought it was time to make his official comeback to the fighting scene once more!

During the progress of the tournament, Heidern tracked down the movements of NESTS, and also took special care in Whip's actions as she teamed up with her lost brother K'. Heidern followed the tracks of NESTS up to the point where the winning teams met inside a flying blimp, where the final battle was supposed to be hosted. Heidern knew for sure that it was a trap used by NESTS to lure the winners into their inminent death. But Heidern trusted the warriors would defeat the evil within NESTS, and his wishes came true when NESTS main HQ, their space station, fell into the ocean. Heidern inmediately sent a reconissance squad to the crashing site of the NESTS space base after the fighters had been placed in a safer place. The report confirmed that most of the base was still kept intact after the crash, which helped Heidern resolve that they could investigate on that basis. But what bothered Heidern, was the report confirming that his dear Whip was yet another clone brewed by the evil technology of NESTS. Heidern must now start worrying about the fate of those close to him, instead of looking after the world.

Heidern is a lonely man, and passes most of the time enclosed in his office and meditating. He sees in Leona the chance to start all over, and get over the death of his family. His old friends, Ralf and Clark, are also with him and make him feel good in those grim moments. Heidern, even after Rugal's death, still feels pain in his heart, but decides life goes on, and his soldiers are the only family he now has.