Nightwing
Although Nightwing is commonly associated with Batman, the title and concept have origins in classic Superman stories. The original Nightwing in DC Comics was an identity assumed by alien superhero Superman when stranded on the Kryptonian city of Kandor with his pal Jimmy Olsen. Drawing inspiration from Batman and Robin, the two protect Kandor as the superheroes Nightwing and Flamebird. Following the Crisis on Infinite Earths continuity reboot in 1985, Nightwing was re-imagined as a legendary vigilante from Krypton whose story inspires Dick Grayson's choice of name when he leaves behind his Robin identity.
Nightwing
Following this, Nightwing decides to leave the team again, due to the events of the "Batman R.I.P." storyline, and due to Batman's apparent death, Nightwing feels his attention should be better aimed at protecting Gotham City.
As a precursor to "Batman R.I.P.", at the New York Comic Con 2008, DC Comics gave away pins featuring Nightwing, Jason Todd, and Hush with the words "I Am Batman" beneath them.
During the storyline, Nightwing is ambushed by the International Club of Villains. He is later seen in Arkham Asylum, frothing at the mouth and presumably drugged, believed by the staff to be Pierrot Lunaire, a member of the Club. Scheduled for an experimental lobotomy by Arkham himself, he's spared by the ICoV taking hold of the Asylum, wanting to use him and Jezebel Jet, Bruce's fiancée at the time, as bait.