In the years leading up to his superhero career, Batman has had several important teachers. Each of these instructors, has, in some way or another, influenced the crime-fighter that Bruce Wayne has become. While Batman's worst teacher, Mister Whisper, left a lasting impression, he ended up becoming one of Gotham's most terrifying villains as well.
Mister Whisper's reign of terror commenced during the "Gothic" storyline in 1990's Batman: Legends of the Dark Knight #6-10, by Grant Morrison, Klaus Janson, Steve Buccellato and John Costanza. Whisper was a serial killer who targeted members of Gotham's organized crime families. Part of what made Whisper such a disturbing villain was how he'd taunt his victims with passages of poetry. Additionally, Whisper got Gotham's criminals so scared, they used the Bat-Signal to call Batman. This was a pretty bold move, considering it was Batman's intention to scare criminals.
Yet with Mister Whisper in town, the Dark Knight seemed to be a friendly face by comparison. Not only did Whisper recite poetry while he viciously killed his targets, he also had no shadow, and was seemingly immortal. These two haunting features made Whisper a truly menacing figure. Apparently, organized crime members thought that they had killed Whisper 20 years earlier. However, Whisper came back to exact vengeance on those who tried to kill him.
Moreover, Mister Whisper held a dark connection to Bruce Wayne. Before he was seemingly killed by the mob, Whisper was the headmaster of a boarding school, attended by a young Bruce Wayne. Whisper harshly disciplined Bruce, among other young boys. Additionally, Whisper murdered a few of these children, which started his career as a serial killer. This personal link to the Caped Crusader made Mister Whisper an even more frightening villain since even Batman was afraid of him. During his investigation, Batman also discovered that Mister Whisper had been alive for 300 years after making a deal with the Devil. Whisper's supernaturally long lifespan was just another factor making him even more terrifying than Batman.
When the Dark Knight tracked Whisper down to a cathedral in Gotham, he found that Whisper planned to release a plague on Gotham, exchanging thousands of souls for a longer lifespan. Batman fought Mister Whisper until Whisper was hit by a subway train. Even this didn't kill him, however. Whisper was only stopped when the Devil arrived at his apartment, dragging him to Hell.
Mister Whisper ultimately succeeded in becoming a supernatural figure that terrified criminals in a way that Batman wished he could. Even in death, Whisper couldn't be stopped by conventional means. The Devil himself had to claim Mister Whisper, as no other force could kill him. This truly made Mister Whisper the type of supernatural figure that Batman wished criminals to perceive him as. Whisper was also a villain who scared criminals in a way that Batman really couldn't. Mister Whisper actually killed his victims, unlike Batman, in such an unsettling way that criminals felt no choice but to turn to the Caped Crusader for help. Whisper's methodology put him more on the level of Gotham's super-criminals, such as the Joker.
With his immortality, Whisper created a legend around himself that Batman couldn't by making his reign of terror last for hundreds of years. Even when the mob tried to kill Whisper, they couldn't, reminding them of the paranormal forces they were dealing with. Most importantly, Mister Whisper shared such a deep, personal history with Bruce Wayne. This troubling connection got into Batman's head, haunting him throughout this case. Even Batman, whose whole goal was to strike fear into the hearts of criminals, couldn't help but be afraid of Mister Whisper. In terrifying Batman, Mister Whisper became one of Gotham's most horrifying villains, scaring everyone in a way Batman simply couldn't.