Warden Ranken was the corrupt Warden for the prison airship, Iron Heights Penitentiary.
Before Arkham Knight Incident
Before October 27, Ranken and his men had tracked down Croc at the Ace Chemicals Lighthouse and proceeded to subdue him, although not before they gave him minor injuries in the process. Ranken then began experimenting on Croc, and realized that his regeneration factor was remarkable, as it allowed the serial killer to recover from any wounds, up to and including forced amputation via buzz saw.
Around October 28, Croc's arm had fully recovered, with further surgeries being scheduled to see the full extent of his regeneration factor.
On October 29, the tests were successful enough that Ranken intended to splice various prisoners' DNA with that of Jones, hoped to replicate Croc's regeneration factor, and also awaited for the recombination of the DNA to stabilize before continuing.
By October 30, however, Ranken ran into a problem with the tests: Namely, the tests had taken their toll on Croc and caused him to radically mutate to become even more bestial than he already was, more monster than man, as a side-effect of the trauma induced by the experimentation's via adaptation responses. In addition, the tranquilizers were no longer having any effect on the bestial serial killer, which meant that Ranken was forced to consider terminating Croc.
On October 31, however, around the time that Ranken was giving a video log that detailed the experiments, Croc proceeded to escape captivity, and managed to sabotage the engines of the prison airship. As a result, Ranken ended up trapped underneath a grate with it quickly flooding with water as a consequence of it crashing into the Gotham Bay.
Arkham Knight Incident
Upon being saved by Batman, who came to the airship to investigate the cause of the crash as well as attempt to apprehend Croc, Ranken demanded that he get them out of there and leave the place to sink, though Batman was adamant in apprehending Croc first. Ranken was about to protest when he was suddenly grabbed by Croc and abducted by him, with Croc also causing a jail breakout by the prisoners in order to ensure that Batman and Nightwing could not pursue and stop him. However, Batman began suspecting that there was more to it than the warden had let on, especially when Croc just abducted him rather than just devoured him then and there.
Ranken was then hooked up to a machine and demanded by Croc to reverse the worsened condition, but the warden was adamant that they couldn't reverse it because it was a result of adaptive trauma, although Croc and the other prisoners did not believe him at all and strongly implied that they would torture him for the information. However, after Batman interfered, Croc forced his contraption through a door to clear off enough room to fight the Dynamic Duo with the various prisoners.
Afterwards, Batman opened the door and released the warden's restraints, with the warden thanking Batman for stopping Croc and implied that they should kill him. However, Batman, who by that point, knew the truth about Ranken's unethical experimentations on Croc and the various prisoners, rebuked him, and told him that he was the true monster there. Ranken then demanded that he let him go, and upon being confronted with the knowledge of his experimentation, stated that he wouldn't beg for forgiveness, with Batman stating that he can only forgive anyway when he didn't commit the crimes that he commit, before he knocked him out. Ranken was then loaded onto the Batwing along with Croc and taken to the GCPD Lockup, where he and Croc were then processed into the GCPD's Maximum Security West Wing Holding Cells. Ranken was then locked up in a cell with the Iron Heights Prisoners. Ranken then tried to tell Batman that he was trying to protect the country while Batman was more concerned about protecting the prisoners and the warden's ties with Quorum, while Ranken derogatorily referred to them as animals before he interrupted himself when he realized that his cell was right next to Croc's and begged Batman to let him out of there as he didn't want to be next to Croc.
Batman then demanded to know the names of who specifically hired Ranken for experimenting on Croc, as he learned about the Quorum's involvement in his capture and experimentation of Croc. Ranken, however, smugly told him that he wasn't concerned with the Caped Crusader's wants before he told him to run along. Batman vowed that he'd talk eventually as "they always [talk]." Ranken then smugly told the Dark Knight that he loved invalidating a flawed hypothesis due to him being a scientist. Croc later asked whether Ranken would ever get justice, with Batman saying that he'd get justice, although Croc was not satisfied, as he wanted to kill him as payback for what he did to him.
- Ranken was only identified by name once, by Prison Officer Burfitt, who explained why they had held Croc prisoner and alluded to his experiments on him. Ranken was only identified as "Warden" in the subtitles, even after the player completed the mission.
- If the player completed the mission after the main story-line, Ranken acknowledged Batman and Bruce Wayne as being one and the same, and even attempted to do a psychological evaluation for Batman's motives only to declare him insane.
- Ranken is voiced by Dee Bradley Baker. Baker also provided the voice for Ra's al Ghul.