Damian Wayne is a DC Comics superhero created by Grant Morrison and Andy Kubert, best known as Batman's biological son—and, more controversially, as the fifth person to take on the Robin mantle.
He's the product of Bruce Wayne and Talia al Ghul, daughter of the notorious villain Ra's al Ghul. Talia kept his existence completely hidden from Bruce for years, faking a miscarriage and ending their relationship to do it. When she finally dumped him on his unsuspecting father's doorstep in 2006's Batman #656, it turned out the al Ghuls had been grooming Damian for a specific purpose: to eventually kill Bruce and take over both the Wayne empire and the League of Assassins, thereby merging the two factions under their control. He was literally designed as a replacement heir.
As Bruce's youngest child and only biological son in main continuity, Damian has four older adoptive siblings: Dick Grayson, Jason Todd, Tim Drake, and Cassandra Cain.
The character has roots going back further than his official debut. An unnamed infant appeared in the 1987 story Batman: Son of the Demon, though it wasn't considered canon at the time. Various alternate universe tales explored the concept before Morrison solidified him as Damian Wayne in the "Batman and Son" arc, kicking off with Batman #655.
When he arrived, Damian was a violent, arrogant kid—trained as a killer by the League of Assassins from childhood. That training put him constantly at odds with Bruce, whose whole thing is refusing to kill. Still, Bruce cares about him, even if he didn't ask for a preteen assassin son. By age ten, after the events of Batman R.I.P. and Battle for the Cowl, Damian became Robin, initially working with Dick Grayson before eventually partnering with Bruce again once Bruce reclaimed the cowl.
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