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.
Jason Todd
Jason Todd resurfaces following the "One Year Later" period, patrolling the streets of New York City as a murderous version of Nightwing. However, Jason shows no intention of giving up the Nightwing persona when confronted by Dick Grayson, and continues to taunt his predecessor by wearing the costume and suggesting that the two become a crime-fighting team. Not long after the two Nightwings meet up, Todd is captured and imprisoned by local mobsters Barry and Buddy Pierce. Grayson reluctantly rescues him, and the two join forces to defeat the Pierce Brothers. Shortly afterward, Todd leaves New York City and the Nightwing mantle to Grayson, along with a telegram telling Grayson he has returned to normal and still considers himself a gift from Batman.