While the most prolific character to hold the mantle of Nightwing has always been Dick Grayson, the former Boy Wonder is far from the only DC Comics figure to use the moniker of the masked crimefighter. Grayson wasn't even the first hero to become Nightwing in the DC Universe since he borrowed the name from a figure in Kryptonian mythology.
With a bunch of copycat Nightwings currently active while Grayson struggles with his own identity issues, here are all the characters to hold the mantle of Nightwing in the main comic book DC Universe.
SUPERMAN
Two figures that loomed large in Kryptonian mythology were the deities Nightwing and Flamebird, who were destined to fall in love and tragically perish only to be reborn in fire, much like the legend of the phoenix. As Superman and Jimmy Olsen find themselves trapped in Kandor in 1963's Superman #158 by Edmond Hamilton and Curt Swan, they decide to take on new costumed personas inspired by and named after the mythological Kryptonian birds.
Prior to Crisis on Infinite Earths, Batman and Robin would team up with Superman and Jimmy in Kandor, with Grayson inspired by their adventures to take on the mantle of Nightwing for himself after leaving behind his Robin persona. While this team-up no longer existed after Crisis, Superman would recount the story of a similar Kryptonian crimefighter that used the Nightwing name, leading to Grayson to develop his new persona.
VAN-ZEE
Created in 1960's Superman's Girlfriend, Lois Lane #15 by Otto Binder and Kurt Schaffenberger, Van-Dee was Superman's cousin from the bottled Kryptonian city of Kandor. Upon his emergence into the outside world and restoration to normal size, Van-Dee fell in love with Lois Lane but deferred to his cousin for her affections. Instead, Van-Dee married a rich heiress named Sylvia DeWitt and had two children with her before the family returned to Kandor.
Back in Kandor, Van-Dee would take on the mantle of Nightwing from his cousin to defend the Kryptonian city. Van-Dee took on reformed criminal Ak-Var to serve as his sidekick Flamebird, with the heroes protecting Kandor until the continuity revisions by Crisis on Infinite Earths erased them and their history in the modern DCU.
POWER GIRL
Following the Infinite Crisis, the DCU saw a one-year time jump while the immediate aftermath was explored by the weekly comic book series 52. The villainous Ultraman posed as Superman and made off with Kandor, with Power Girl and Supergirl volunteering to defend the Kryptonian city from his and Saturn Queen's machinations.
Depicted in the pages of Supergirl, Kara Zor-El became Flamebird while her Earth-2 counterpart became Nightwing to defend Kandor. This would result in the two superheroes becoming estranged for a time after Saturn Queen coerced Supergirl into abandoning Kandor and the mantle of Flamebird while the city was still in dire need of her help.
LOR-ZOD
Created by Geoff Johns, Richard Donner and Adam Kubert in 2006's Action Comics #844, Chris Kent was adopted by Clark Kent and Lois only to discover he was sent by his biological parents General Zod and Ursa as a gateway between Earth and their prison in the Phantom Zone.
Chris would reemerge prematurely aged into early adulthood through his connection to the Phantom Zone following Kandor's restoration into the city-state New Krypton. He took on the mantle of Nightwing while the Kryptonian soldier Thara Ak-Var, created by Johns, James Robinson and Renato Guedes in 2008's Superman #681, joined him as the new Flamebird. The two would use their powers to protect Earth from Kryptonian sleeper agents culminating in War of the Superman.
NITE-WING
Created by Chuck Dixon and Scott McDaniel in 1997's Nightwing #8, Tad Ryerstad was one of the first figures to surface after Grayson set up shop in Bludhaven. As a sociopathic young man that idolized crimefighters, Tad would openly use lethal force in a misguided attempt at his own vigilanteism, taking on the moniker Nite-Wing after a late-night chicken wing restaurant.
Unaware of the full extent of his mental condition and violent tendencies, Grayson trained Tad for a time. After killing an undercover FBI agent, Tad's mental condition worsened, which led him to kill the corrupt police force that had illicitly supported him. Eventually, Tad was locked up for good after being implicated in multiple murders.
CHEYENNE FREEMONT
Created by Bruce Jones and Joe Dodd in 2006's Nightwing #118, Cheyenne Freemont was a fashion designer living in Manhattan that was introduced as a romantic interest for Grayson while he lived in New York City following Infinite Crisis. After relocating, Grayson learned that Jason Todd -- still openly employing lethal force in his own crimefighting -- had created a makeshift Nightwing persona of his own and was similarly operating out of New York.
Cheyenne was revealed to be a metahuman with powerful psionic abilities that attempted to keep her superpowers a secret in an effort to live a normal life. After Jason was kidnapped by two strange metahumans, Cheyenne decided to help Grayson by designing her own version of Nightwing's costume before retiring from the superhero game for good after Jason's rescue.