Ratcatcher

Once employed as an actual rat catcher in Gotham, Otis Flannegan soon started using his natural gift - an affinity with and ability to control rats - to stage a variety of crimes. Eventually his control over the vermin grew until he threatened Gotham City with a veritable army of rodents. Incarcerated many times at Blackgate, he's able to do as much damage within prison as outside, using his loyal pets to relay messages and transport materials inside the maze of ventilation ducts that wind throughout the giant prison.

Before Arkham Origins Incident
Otis Flannegan had his own exterminating business. By this time, he had already started wearing a suit and manipulating Gotham's toxic rats in order to help Roman Sionis take over Gotham.

Arkham Origins Incident
Ratcatcher's gear could be found at My Alibi in Coventry. During this time Otis Flannegan's criminal career went unnoticed to the point he hadn't even made a reputation for himself and had made a name for himself yet.

Cold Cold Heart Incident
Ratcatcher's gear could be found at GothCorp.

Between Arkham Orgins and Arkham Asylum Incident
At one point, he may have been transferred to Arkham Asylum for psychological treatment.

Road to Arkham Incident
While at Arkham, he was presumably under treatment of Dr. Young, as she possessed notes on his behavior. His gear was taken away from him, but he appeared to have retrieved it and had hidden it in a ventilation shaft for him to use when he was able to get to the Botanical Gardens.

Arkham Asylum Incident
The Ratcatcher fled Arkham Island in the confusion of the takeover, leaving in such a hurry, he was unable to retrieve his gear from the Botanical Gardens. Ratcatcher was one of the few villains to escape Arkham during that event along with Tweedledum and Tweedledee, Great White Shark, Maxie Zeus, Riddler, Mr. Freeze, Penguin, Catwoman, Killer Moth, Calendar Man, Ventriloquist, Firefly, Humpty Dumpty and Black Mask. Ratcatcher's gear can be found in a vent in the Gardens.

Between Arkham Asylum and Arkham City Incident
Somewhere between Joker's takeover and the Arkham City Incident, Ratcatcher was apprehended and incarcerated into Arkham City.

Arkham City Incident
The Ratcatcher did not appear in-game, although he was mentioned as being locked up in Arkham City and hiding, in fear for his life. He figured that he could sell items that his rats found in the sewers of Gotham, and created a small market. That attracted the Penguin's attention, and some time later, Flannegan was dragged into the Museum, screaming for his life. Penguin's Gang mentioned that he was supposed to have ironically been eaten by his rats, but after they ignored him for several days, Penguin tossed Ratcatcher to his shark, Tiny, who presumably ate him. While it was believed by some that he was dead, a conversation in the game could be heard between two Thugs discussing another thug being eaten alive by rats, alluding to the possibility that Flannegan was still alive. He was also mentioned in a riddle that could be found in the Industrial District. Some of Penguin's Henchmen were known to have been fed to Flannegan's rats.

Later, Ratcatcher participated in a kangaroo trial against Joker held at the Solomon Wayne Courthouse. When put on the stand by Two-Face, Ratcatcher revealed that he had been psychologically tortured by Joker when the Clown Prince of Crime poured toxin upon his rats right in front of him. When Batman interrupted the proceedings to stop Joker from being executed, Ratcatcher was one of many who attempted to kill the Joker. In the ensuing melee he sent his rats to attack Joker's henchmen.

Before Arkham Knight Incident
It was revealed that Ratcatcher suffered significant injury from his fateful encounter with Penguin, losing his left eye and arm in the process. After Hush, disguised as Bruce Wayne, entered his domain with two police officers, Ratcatcher sent his rats to attack them, managed to kill the officers, and incapacitated Hush. Before the rats could kill Hush, the Arkham Knight came down with a knee to Otis' face, and put him to the ground. The Knight then used an intense taser to fry Ratcatcher and his rat minions alive. Batman later arrived at the scene of the crime and discovered Otis' charred corpse.

Ratcatcher
Real Name: Otis Flannegan

GCPD Profile
Otis Flannegan

Batman's Database Profile
Flannegan

Dr. Penelope Young
TELL MAINTENANCE TO INCREASE RAT POISON AROUND CELL.

Psychological Profile: Suffering from acute anthropomorphic delusions, Flannegan is so convinced that he can control rats, that he has persuaded many of Arkham's inmates, orderlies, guards, and even other doctors that he commands this fantastical ability. Personally, I don’t consider "evidence" provided by the Batman to be convincing of anything, and find it much more likely that Flannegan has manifested a unique variation of a Messiah complex.

Additional Notes

I'm hesitant to administer aggressive treatment before first doing a full write-up on his condition; it could be an easy way to get published and procure naming rights to a newly documented disorder.

If only there weren't so many odious vermin constantly swarming in his cell.

Attributes

 * Thorough knowledge of Gotham's sewer system and Blackgate Prison's layout
 * Eerie ability to wordlessly communicate with and command all rats
 * Overvalues rodent life, especially in comparison to human life

Quotes
Main Page: Ratcatcher/Quotes

Trivia

 * Ratcatcher's gear could be found inside a ventilation shaft at the Botanical Gardens. Scanning that unlocked his biography.
 * His gear could also be seen in the backstage area of "My Alibi" in Arkham Origins.
 * Ratcatcher was one of the many villains to have a biography in Arkham Asylum and many references in other Arkham games, without physically appearing in them (other examples included Killer Moth and Great White Shark).