39 years ago - Kirk Langstrom is born.
21 years ago - 18-year-old Kirk goes to college.
17 years ago - 22-year-old Kirk begins grad school.
14 years ago - 25-years-ago Kirk marries his wife Francine
13 years ago - 26-years-ago Kirk begins his research, developing new ways to extract genetic markers from bats with the intention of giving disabled humans access to sonar.
12 years ago - 27-year-old Kirk, with his wife Francine pregnant and his hearing diminishing, treats himself sucessfully but slowly mutates into Man-Bat. He is saved from himself by Batman, and Francine is able to administer a cure.
10 years ago - 29-year-old Kirk earns his doctorate.
9 years ago - 30-year-old Kirk fears he is regressing when the Man-Bat begins to appear again in Gotham. Eventually he and Batman discover that Francine has been accidentally dosed, and are able to cure her.
6 years ago - 33-year-old Kirk's cure fails and he mutates again into Man-Bat. Once he is captured by Batman, Pieter Cross consults on a new cure.
3 years ago - 36-year-old Kirk's son Aaron begins the mutate into a bat-creature, but seems to have a greater degree of control. He is administered regular medication against his condition and monitored.
2 years ago - 37-year-old Kirk is forced to hand over all his research and forumlas to the League of Assassins when Nyssa Al Ghul kidnaps his son.
While some villains have complex psycological motivations and others are centered more around their specific powers, there are also characters that are simply classic story tropes all on their own. Man-Bat is such an obvious antagonist for Batman that it's kind of odd that it took 31 years before someone thought of it, but at his core he's a very easy to follow classic sympathetic monster story. It's something that might stand out as a little hokey if it wasn't in a comic book, but it fits so well into the larger mythology of Batman that he's a welcome addition to his gallery of badguys.
Man-Bat's Comic History
Man-Bat first debuted in 1970 right in the midst of Neal Adams and Julius Schwartz's ongoing efforts to modernize and de-campify the Batman mythology. This is the same era that brought is Ra's Al Ghul and other more serious enemies for Batman to battle. It was a simple alegory of a classic monster tale, but that sort of story is very much a part of Batman's DNA, and it was a good fit. Man-Bat actually had his own series five years later, but it was canceled after only two issues.
The character doesn't really lend himself to showing up TOO often, because if he's to be used properly his appearance means that something has gone wrong with Langstrom, and that needs to be adressed anew each time. This was actually true of early Batman villain Two-Face originally, as well; Harvey Dent was actually healed through plastic surgery at the end of each appearance so that each new regression into his life of crime meant he had to be scarred again. This might have worked back in the 40's, but Man-Bat was in a slightly more serious comic era and that kept his appeances limited.
Of course, as time went on, this mattered less and less. he's become a commmon background character, having appeared in various crossover books in crowds of villains, which might drive up his total number of appearances but undermines the core of his tragic monster story.
Our Man-Bat Story
The idea of Man-Bat is, admittedly, a little on the nose. While in application, Man-Bat is a monsterous allegory for Batman that came about in an era that was trying to get rid of the Adam West-era campiness, It's difficult to completely ignore that this is an entirely new flavor of monster movie campiness all on it's own.
It's actually within that monster movie vein that the character really shines, however. Man-Bat is a creature of instinct, he's not malicious. The person inside that monster, Doctor Kirk Langstrom, doesn't want to BE a monster. He doesn't need to be defeated, he needs to be helped. This is actually something kind of rare within the Batman mythology; for a character that really does want to help people, a preponderance of what we see him doing is fighting people. It's actually cool to see stories where he might be deploying his particular Bat-tactics, but it's all in an effort to save someone from themself.
We wanted to make each new recurrence of the Man-Bat a specific evolution of the character, rather than make him just a generic badguy who showed up sometimes. Many of these versions of the character come from some of the seventies and eighties appearances of the Man-Bat, as well as from the Animated Series. Later versions made him a more generic villain, but that really does him a disservice.
One of the very first things Grant Morrison did when he started his run on Batman was to introduce the idea that the League of Assassins had gotten their hands on Langstrom's Man-Bat formula and created a small army of ninja Man-Bats. It's such a clever evolution of the concept, because while Langstom is still a redeemed and sympathetic character, it allows the specific idea of the Man-Bat to evolve.
In fact, it actually puts us in mind of a possible way to evolve the story even further. Langtrom's son Aaron is still only 11 or 12 at the end of this story, but it's understood that he was effected by his parent's use of the Man-Bat formula. Rather than simply make him another monsterous mutation that needed to be caught, we instead made gave him a greater degree of control over his transformations.
So, at some point in the future Aaron Langstrom will live in a world where the League of Assassins is using a version of his father's work to hurt people. Imagining that Aaron (once he gets some fight-training from someone, say, Richard Dragon...) decides he wants to fight the League? Wouldn't that character be an interesting one to follow? He just happens to be the same age as our future Teen Titans...