[u][b]Gotham Knights:[/b][/u] Legacy Batfam who were inspired by Batman but aren’t actually directly connected or mentored by him. A Dick who skipped straight to Nightwing. A Jason who was never Robin before Red Hood. A Stephanie who struck out as Spoiler before ever meeting Bats let alone being fired. Etc. 

[u][b]Dick Grayson/Nightwing:[/b][/u] Aged up. Family killed at Haly's Circus Massacre. Swore to strike back against the murderers. Became Nightwing.

[u][b]Jason Todd/Red Hood:[/b][/u] Drug runner/enforcer for Red Hood Gang. Had 'A Loved One' (idk who). Jason and A Loved One were caught in a drive-by/rival shootout. A Loved One didn't make it, Jason fell into a coma. When he woke up and found out A Loved One died he started a rampage against both his old gang and the rival one for taking A Loved One from him. Wipes out Red Hood Gang and adopts the moniker as the last member there will ever be.

[u][b]Barbara Gordon/Oracle:[/b][/u] Basically the events of Killing Joke, but no pre-existing ties to Batman or career at Batgirl. On recovering, vows to do all she can against the criminal elements and rising supervillains of Gotham to stop anything like this happening ever again. Becomes Oracle.

[u][b]Stephanie Brown/Spoiler:[/b][/u] Father's an asshole who was also Cluemaster. When Stephanie discovered this she was incensed and determined to put a stop to his crimes. She suited up and became Spoiler to defeat him.

[u][b]Tim Drake/Red Robin:[/b][/u] Began researching the Gotham Knights as they became known, eventually figuring out their identities. He approached Dick Grayson (or whoever the 'leader' is) soon after, wanting to help, but was rebuffed. Instead he tracked the Knights for a while, and was able to save them at a critical moment. After this, he joined them, having proved his capability and standing up for himself and his responsibilities. He becomes Red Robin.

[u][b]Cassandra Cain/Orphan:[/b][/u] Raised as a living weapon by her father, David Cain. Was sent to Gotham to kill Miranda and Marcus Row, petty criminals working for the Falcones, as a test. She succeeded in killing Marcus but reading his body language as he died horrified her and marked a distinct psychological shift, breaking out of her father's programming and realizing the evil she had been created for. She rejected her father and cut all contact, vowing to eternally atone for the murder she had committed, adopting the pseudonym Orphan.

[u][b]Harper Row/Bluebird:[/b][/u] Mother and Father (Miranda and Marcus) were petty criminals working for the Falcones. Marcus was an abusive POS to Harper and her brother Cullen; Miranda was slightly better but still sometimes neglectful and cold when her 'work' demanded it. After the attack by Cassandra Cain on her parents, Harper wanted revenge, but after tracking Cassandra and seeing how she'd changed her ways, Harper realized she could also break out of the cycle set by her parents and be a better role model for Cullen. She re-invented herself as a protector and provider, trying to encourage her mom to be better now that Marcus was dead, becoming Bluebird, a symbol of hope, good fortune, and fresh starts.

[u][b]Duke Thomas/The Signal:[/b][/u] Born to single mother Elaine, Duke never knew his father; his mother kept his identity a secret, but when Duke grew up and began exhibiting metahuman abilities, she had to come clean and explain his father was Gnomon, the immortal, who she'd fled from after being taken as a concubine to sire his child. When Gnomon returned for Duke (having known about him the whole time and just waiting for him to come of age), he rejected his father, and in return Gnomon slew Elaine, reasoning that with no mother to return to, Duke would have no choice but to come with him. Well, this didn't change Duke's mind, and instead the two fought across Gotham until Gnomon was finally defeated and repelled. Duke swore to honor his mother and disavow his father by using his powers to protect the people of Gotham, becoming The Signal.

[u][b]Helena Bertinelli/Huntress:[/b][/u] Born to the Bertinelli Mafia crime family, Helena was subject to beatings from her father, aloofness from her mother, and constant threat from rival crime families who saw her as a weapon to be used against her family. As she grew, her hatred of everything the Bertinellis were and stood for grew with her, erupting to a bloody climax when an assassin broke into the Bertinelli house one night to kill Franco, and was discovered by Helena, who took the opportunity to kill her entire family and then the assassin, positioning herself as the only survivor of a horrific attack. Sent back to Sicily to live with the 'Old Family' where she'd be 'safe', she instead spent years training and preparing, and as soon as she could, travelled back to America to finish what she'd started: wiping the Bertinelli Mafia, and any other mob besides, off the face of the Earth, as Huntress.

[u][b]Bette Kane/Flamebird:[/b][/u] An LA darling and tennis prodigy, Bette was visiting Gotham as part of a tournament when she witnessed Nightwing (or whichever other Gotham Knight) engaging in crime-fighting, and became infatuated. She trained in gymnastics, athleticism, and martial arts, and then took a hiatus to travel back to Gotham and debut as Flamebird, vying for Nightwing's (or whoever's) attention. While flattered, the young vigilante was also uncomfortable with her obssession and rejected her reasons for becoming a vigilante, ultimately denying Bette's advances. Dismayed, Bette returned to LA, but found tennis, debutante balls, and schoolwork now very hollow compared to the thrills and triumph of vigilantism, and ultimately decided to abandon her shallow life altogether and go back to Gotham as Flamebird to continue the fight and find true fulfilment. 

[u][b]Charlotte Gage/Misfit:[/b][/u] A natural-born Metahuman to a single mother in Metropolis, Charlotte was caught in a fire at a young age. Her powers manifested - the ability to teleport, but only able to bring inorganic matter with her - and while she was able to save herself, she was forced to leave her mother behind. She managed to get help, but too late; her mother perished in the fire. Orphaned, Charlotte spent her formative years 'jumping' across the US, able to keep herself fed, sheltered, clothed, even enjoy luxuries, but ultimately still just a homeless drifter. Eventually she caught wind of the Gotham Knights, particularly [female members] and found herself spying on them, a secret admirer. After 'jumping' into Oracle's hideout and taking Barbara by surprise, subsequently learning the Knights' identities in the process, the Knights agreed to take Charlotte in as her surrogate family. She took the name Misfit and began to use her powers for altruism.

[u][b]Katherine Kane/Batwoman:[/b][/u] Born to Gabrielle and NATO Colonel Jacob Kane, Kate and her twin sister Elizabeth lived a good life until their twelfth birthday, shortly after which they and their mother were kidnapped by international terrorists as a strike against her father. Though Jacob managed to mount a rescue mission, Gabrielle was executed and Beth was killed in crossfire. After this, Jacob retired and moved himself and Kate to Washington, doing his best to be a good father while intensely grieving, and also starting Kate on a gruelling regimen of self-defence, military conditioning, and tactical training, in an effort to prevent her from ever being vulnerable again. After being forced out of military service due to a lesbian scandal, Kate moves to Gotham and falls into a party life, during which she meets and begins a relationship with GCPD officer Renee Montoya, who's also assigned to the for-show Batman Taskforce, the work of which begins to fascinate Kate. When Kate is mugged during a phonecall argument with Renee over her hard-partying lifestyle, she uses her military training to defend herself, and abandons the thug on the steps of the GCPD; the next day Renee mentions how 'the bat' must have delivered him and how he turned out to be a prolific rapist and ganger, and Kate feels pride and purpose swell within her as well as a sense of vengeance for her mother and sister, and ultimately decides to follow Batman's example and become Bat[i]woman[/i], abandoning her lifestyle and sobering up to carry on bringing criminals to justice.

Abyss?
Circus of Strange?
Clayface I?
Cluemaster (if running Spoiler)?
David Cain (if running Orphan)?
The Flamingo?
Lock-Up?
Magpie?
Miracle Molly (if running Oracle)?
Punchline (if running Bluebird)?
Ratcatcher?
Ten-Eyed Man?