Warning: contains spoilers for The Joker #13!
The Robin. This is revealed in The Joker #13. The issue comes from James Tynion IV and Giuseppe Camuncoli.
This series has the Joker on the run while being chased by commissioner Gordon and the Batman villain Bane. Eventually, the Joker finds himself in Texas - the prisoner of a family of Texas Chainsaw Massacre-style cannibals who plan to eat him. Thankfully for the Clown Prince of Crime, the family's meal is interrupted as Bane's clone-daughter Vengeance storms their compound. She's looking for Joker, eager to fulfill her desire to kill him - one implanted in her by her creators.
With the family largely defeated, Vengeance and Joker meet, and she instantly threatens to kill the clown. Of course, Joker laughs in her face, taunting her to kill him. The Joker's mocking gets pretty specific, too, when he brings up the fact that Vengeance was grown in a test tube and is only a year old. Joker finds this fact hilarious because after everything he's done and all the times he came close to death, he's about to be killed by someone who doesn't have any real reason to want him dead, and who is technically only one year old. "See, that's how I hope they it," he exclaims. "Did you know that Joker got killed by a giant baby?"
While this meaningless death would be fitting for the nihilistic villain, it's also eerily similar to how Damian Wayne died. Though he's since been resurrected, Batman's son was originally killed by the Heretic, who was a clone of Damian. What's even stranger is that when the Heretic's helmet comes off it's revealed to have the face of an infant. This is due to him being artificially aged. So Damian was likewise killed by a giant baby, the same way that Joker hopes to be ed. It's a twisted irony that even when he's not being deliberate, Joker's perfect death still echoes perhaps Batman's most painful moment.
The connection between the Joker's death and a Robin's death will always be strong as the Joker was the first person to infamously kill a Robin. It's therefore fitting that Joker would want to perish like the Boy Wonder, even if it is a weird twist that his desired end echoes Damian's, rather than Jason Todd's. As Bane arrives to stop Vengeance killing Joker, it seems he won't actually get the death he craves, but Batman would likely be disturbed to know that Joker was so happy to meet the grisly end previously reserved for his son, Robin.
