Joker shoots Barbara Gordon. The injury that paralyzed her, ended her career as Batgirl & paved the way to her becoming Oracle (from the graphic novel Batman: The Killing Joke by Alan Moore and Brian Bolland)
Dick Grayson (aka) Nightwing and Barbara Gordon (aka Oracle/Batgirl). They've shared a close bond since they were young partners to Batman. Despite both of them facing many trials, including Barbara's paralysis for an extended time due to a spinal injury, this bond has remained intact.