Nightwing

Raised by his parents, the "Flying Graysons", in a circus, Dick Grayson was trained to be incredibly athletic. Excluding Dick, the Flying Graysons were killed after criminals failed to extort the circus. Dick Grayson was soon adopted by billionaire Bruce Wayne, whose secret was discovered by Grayson one day. Shortly afterward, Grayson was extensivley trained to become Batman's sidekick, becoming the first Robin. Aiding Batman for years, Grayson managed to break away from him and become something more than just a sidekick. Donning the identity Nightwing, he patrols both Gotham City and Bludhaven, his new home, assisting the Dark Knight not as an apprentice, but as an equal.

After Arkham
Nightwing is seen alongside Batman investigating the mysterious Abramovici Twins, who he had heard stories about during his Flying Grayson days with his parents, and along Batman, concludes that Thomas Elliot did their seperation.

Batman: Arkham City
Nightwing stayed in the Wayne Manor while Batman was in Arkham City and defended it from robbers who were trying to ransack the mansion. During Protocol 10, Hugo Strange had sent a number of TYGER soldiers to Wayne Manor to kill Batman's allies and uncover his secrets, but luckily Robin and Nightwing, who were training in the Batcave, came to the rescue and were able to defeat the TYGER guards until the police arrived.