Ghost-Maker's History
Origins
Minhkhoa Khan was the son of a wealthy Singaporean business owner in the exports industry. When he was eight years, a psychologist diagnosed him as a psychopath, as he was unable to feel empathy or fear. His family was physically threatened until they sold their company to the uber-wealthy Midas crime family. Determined to destroy the Midas family and make them feel the worthlessness they tried to push on his parents, Khoa set off to become a crime-fighter and get revenge.
Khoa's goals caused him to cross paths with Bruce Wayne as they trained with many of the same mentors, and the two struck up a friendship. However, their connection became strained after Bruce told Khoa that the reason he wanted to become a crimefighter was to avenge his parents; supposedly angry that he was doing it for emotional reasons and not for the art of it, Khoa attacked him.
Over the years, Khoa would fight Bruce many times as their paths crossed during their journeys; Bruce would later claim that once he turned 20 years old, he won these fights every time. One of these fights occurred after Khoa followed Bruce to Dublin and clashed over the right to learn from Tommy Tivane, the world's greatest knife-thrower. Khoa also seemed to have harmed a mutual master in Morocco, souring their friendship further. He later trained with the Desert Kings in the Gobi Desert for two months; when Bruce went there the next year, he followed him and tried to initiate another fight. Bruce rejected him, as it was the anniversary of his parents death and he wished to be alone, but eventually relented after Khoa claimed that this sentimentality made him weak.
Despite his nature and their disagreements, Khoa was concerned for Bruce and stopped him in Argentina before he left back for Gotham City in a last attempt to appeal to him. Khoa implored him to realize that there is no way he can save everyone, and that operating with this singular focus would eventually wear his soul down to nothing. He asked Bruce to instead join him in southeast Asia where they would systematically destroy criminal underworlds, offering to do the same to Gotham once they had the resources. Disgusted with Khoa's outlook, Bruce warned him not to come to Gotham and Khoa agreed, as he had no interest in the city; in return, it was agreed that Bruce would not step foot where Khoa was operating.
Taking the name "Ghost-Maker", Khoa followed through with his plan; mostly operating within Southeast Asia, he would spend a year taking down criminal operations in whichever city he went, leaving a massive body count and no trail for authorities to discover him. While operating in Singapore, he would eventually cross paths with Bruce (now operating as "Batman") when he tracked down a Gotham criminal who had fled there. Batman begrudgingly agreed to allow the latter to handle the criminal, per their agreement; on the way back, Bruce would confide to his protégé that although he was still furious with Ghost-Maker's selfishness, he also missed being friends. He later tracked down Ghost-Maker and offered him a position within Batman Incorporated, but this enraged him and resulted in another fight.
Eventually, Khoa obtained his long-awaited revenge on the Midas family by taking down Madame Midas, the family's current head. As he defeated her, he repeated the same gloating words she had told him the day his family was attacked.
Fighting for Gotham
After the Joker War, Ghost-Maker broke the pact in order to step into Gotham as its new protector, disappointed in how Bruce handled its criminals. He activated his Ghostnet to absorb and analyze all the network infrastructure of Gotham's criminal underworld, and begun processing an action plan to dismantle it. He soon found that a new vigilante was his main obstacle in applying this plan -- a teenager named Bao Pham, going by the alias of "Clownhunter". Given the fact the boy was also a ruthless killer endangering civilians, Ghost-Maker chose him to be a symbolic victim for Bruce to realize his mistakes.
Upon his arrival, Ghost-Maker killed all of the Grinners, a gang of Joker supporters, at their headquarters called the "Smile Bar". He then located Clownhunter while the latter was trying to blow up Harley Quinn's apartment; Batman came to the boy's rescue and the two engaged in combat. Bruce explained that Bao is a teenager who witnessed his parents being killed by the Joker five years before (a murder that Harley was present for), and that he would rather rehabilitate him than kill or imprison him.
Disappointed that Bruce had not changed, Ghost-Maker tranquilized Bruce, Harley, and Clownhunter and trapped them in a room of Arkham Asylum, leaving only Clownhunter unrestrained in order to force Bruce to handle him. However, the plan did not work as Harley managed to break through to the teenager by explaining her resolve to atone. Batman related that although it was true that not everyone can be saved, caring for people like Harley and Bao allowed them to get better and make a difference. Although Batman has come close to death many times and his work would probably never be done, he believed the success he has had with rehabilitating people over the years prove that empathy has its place.
Satisfied with Bruce's answer for the time being, Ghost-Maker initially intended to leave, but Bruce believed he would need help in a rapidly-changing Gotham and asked Ghost-Maker to stay with him -- as long as he does not kill. Seeing it as an interesting challenge, Ghost-Maker accepted.
Partnership with Batman
The first major case the two tackled was that of the Unsanity Collective, a high-tech, radical transhumanist movement that had been stealing tech throughout the city. As Batman tracked down the organization's leader, Ghost-Maker saved Harley Quinn from the police and brought her back to his base: "The Haunt". Intrigued by Harley, Ghost-Maker questioned her on her ideals and pasts. They were quickly interrupted by Bella Garten and Oracle, the later of whom sent them to help Batman. After saving Batman from the Magistrate agent Peacekeeper-01, Ghost-Maker learned that The Scarecrow had been manipulating the Unsanity Collective the whole time. Alongside Batman and Harley, Ghost-Maker is able to save several members of the Unsanity Collective, including a young child. He protected them again when they were pursued, by the Magistrate, to the underground jungle of Eden. With the Unsanity Collective saved, the Magistrate defeated, and Scarecrow back in prison, Ghost-Maker is recruited to train Clownhunter and the two leave Gotham.