Riddler Thugs

The Riddler's Thugs are thugs and henchmen that worked for the Riddler. Some are disguised as normal henchmen that worked for Joker, Penguin, and Two-Face, while others are very well affiliated with any of said gangs, but also work for Riddler.

Arkham Origins Incident
Batman interrogated thugs who worked for Enigma to reveal all of the Extortion Datapack locations on the map.

Arkham City Incident
After Batman optionally revisited the Church and Medical Center (which was where Aaron Cash and his security team were stationed), he saw that Riddler had kidnapped Cash and his team, took them hostage, and the only way that he could save them was by completing Riddler's challenges. After Batman left, all disguised and undercover Riddler Thugs were highlighted in green and could be interrogated to reveal all of the Riddler Trophy locations and Riddles on the map, much like the Riddler Maps.

Arkham Knight Incident
Riddler Thugs reappeared in Batman: Arkham Knight, and served the same purpose as in Arkham City. The Riddle Robots appeared as well, and were an army of robotic servants that Riddler, by his own admittance, had built himself as a replacement for hiring common thugs. Most of the Riddler Thugs were found on the streets, with a few occasionally found indoors, while the Riddler Robots were exclusively for the Riddler's Challenges at the orphanage. In addition, some of the Riddler Thugs work undercover as soldiers of the Arkham Knight's Militia.

Catwoman's Revenge Incident
The Riddler Thugs were later tasked with guarding the entrance to the Riddler's Robot Factory underneath Winslow's Toy Shop, and three of them each had a card key. However, the Riddler Thugs also implied an interest in backstabbing their employer largely as revenge for replacing them with his robots. They ultimately were taken down by Catwoman, who broke into the hideout with the intention of robbing the Riddler and destroying the hideout as revenge for his earlier holding her hostage.

Trivia

 * Riddler Thugs effectively serve as a replacement for the Riddler Maps found in Batman: Arkham Asylum. It is likely that Riddler switched back to using Riddler Thugs to make things more challenging for Batman. It is also implied that they aid Riddler in setting up the riddles (such as Riddler Trophies) left for Batman around Gotham, explaining how Riddler is able to place them in areas that would be hard or impossible for him to gain access to.
 * The Riddler Thugs were the only gang that didn't show any dress code to represent their alliance. However, in Catwoman's Revenge, they were given a dress code that was identified as green vests with some hoods.
 * It was possible to knock out a Riddler Thug before you interrogated him. However, if the player did so, the game would simply spawn another one somewhere else. In Batman: Arkham Origins, this wasn't actually possible as the henchman fell to the ground and gave up if he was beaten and could still be interrogated. This feature is not present in Arkham Knight, as Arkham Origins was developed by Warner Bros. Montréal. It is likely that this feature was simply omitted by Rocksteady Studios. This might have been also done to add difficulty, as this requires players to pay attention to not accidentally knock them out.
 * However, in Knight, Batman seemingly avoids using instant takedown moves on Riddler thugs if there are other enemies around, unlike in City in which Batman could randomly target and take out the informant too early. In addition, Batman cannot use a fear takedown on a Riddler informant.
 * In Arkham Knight, the Riddler Thugs were less cooperative, which lead to Batman needing to knock them out if he mis-executed a counter.
 * Officer JT Wicker, found at the GCPD Lockup, was identified as a Riddler Thug, but combat was impossible there. While not instructed to do so in game, pressing "counter" made Batman interrogate him.
 * Contrary to the comics, Riddler does not treat his henchmen well. In the comics, he pays them quite well and gives long vacations.