Nightbird (G1)
Nightbird was Megatron's precious cuddle-wumpus in Generation 1 continuity
G1
Nightbird was a robotic ninja warrior created by the "famous scientist" Doctor Fujiyama, ostensibly to show how advanced Human technology had become. The Decepticons stole Nightbird, and Bombshell implanted her with an enhanced brain chip which turned the drone-like Nightbird into a true ass-kicking machine. Nightbird broke into the Ark and stole the Autobots' World Energy Chip, which contained the locations of a variety of energy sources, energy sources that the Decepticons would most assuredly use for conquest!
The Autobots later beat the crap out of Nightbird and took her back to Doctor Fujiyama, who locked her up.
The Chiba Institute of Technology actually built a ninja robot in 2003. Martial arts is used as a benchmark of physical dexterity in robotics.
Various fan fiction authors have paired Nightbord with Megatron as a potential love interest. Though in the cartoon, Nightbird was shown with zero personality or independent thought. Megatron regarded her as a weapon and nothing more.
Wreckers
In 2025 or so, at which point the retard built an entire army of the damn things. Then they killed Daniel Witwicky and Wheelie, an event which caused Arcee to enter a deep depression. Presumably they all blew up or died or something after that. It was never really explained very well, and nobody fucking cares, anyway. The Nightbirds blew up, that is. Not Arcee. She went off and did other stuff.
Dreamwave
In the Dreamwave comics, a science fiction movie Enter the Nightbird featured Nightbird kicking shiny metal robo-ass.
