There is no questioning the fact that the Joker is Batman's greatest enemy. Many say they are opposite sides of the same coin and others say they are actually more alike than either would care to admit. The Joker is Batman's deadliest villain and he's shown many times he won't hesitate to get nasty and make personal attacks against anyone that gets in his way.
Batman has tried to contain the dangers of fighting evil. Despite his many times being reluctant to allow others to stand by his side in the fight, there are many individuals that are part of the Bat Family. Their greatest weakness could be the danger of their secret identities getting revealed. This would allow their enemies to attack and catch them off guard.
The Joker's sanity is often called into question but his times of goofiness are by no means an indication that he is not intelligent. What does it mean when Batman's greatest enemy might be aware of his greatest secret along with the identities of those closest to him?
== TEASER ==Jason Todd
Minor spoiler here. Starting with Jason, we saw in last week's RED HOOD AND THE OUTLAWS #0 that Joker claims to have had a hand in creating the second Robin for Batman.
First of all, this account came directly from Joker so we know there might be some credibility issues with that fact alone. It does offer a conflicting view as to how much he knows about Jason and Bruce.
The idea is Joker realized that Batman needs a Robin. This must have been after Dick left to become Nightwing. Joker was in a situation where he was observing Jason's dad get a bullet removed with Jason tagging along.
When Joker selected Jason as the target of his molding, he made a point with his henchman that he didn't want to know Jason or his father's name.
Despite this, Joker apparently was able to manipulate Jason's life. He was able to observe Jason's dad get arrested, which means he knew where he lived. He dumped Jason's beaten body at Leslie Thompkins' clinic, somehow knowing she had a tie to Batman. And he also knew that all of his actions would lead Jason down the road to becoming Batman's new partner.
It seemed that Joker didn't want to know who Jason was or who the next Robin would be. But if he knew about the connections and followed his own trail of Jason moving in with Bruce and then Batman gaining a new Robin, it'd be all right there in front of him.
Batman
Batman is the big one. During BATMAN: R.I.P., there was a lot of people running around that knew Batman's identity. Bruce Wayne's girlfriend, Jezebel Jet, a famous model, was apparently kidnapped by the Black Glove. As she was being held "captive," Batman removed his makeshift mask as Jezebel was screaming out "Bruce!"
Joker was standing right behind Batman. Joker has had contact with Bruce Wayne before. Even if he didn't care about the romantic liaisons of Gotham's wealthy, he would have to put together that "Bruce" was billionaire playboy Bruce Wayne.
Nightwing
Does Joker also know Dick Grayson's identity? First of all, as Nightwing, wearing a teeny tiny mask may not be the best means to conceal a secret identity. Also during R.I.P., Dick was captured by Black Glove and his little mask was removed. Joker was wandering around during all of this. Dick Grayson is also a prominent member of Gotham's elite. Of course if Joker knows Bruce, he could easily know Dick's relationship to him.
Batgirl
What about Barbara Gordon? We all know that when Joker shot her, he wasn't targeting her. He did it as a way to try to make Jim Gordon crazy. In the pre-New 52, Barbara stopped being Batgirl and retired before she was shot. In the post-New 52, that may not be the case. Since we're looking at a shorter time frame, she could have still been active as Batgirl and forced to retire when she was paralyzed. This along with her hair color and having a crime-fighting father could make reason for the lack of Batgirl running around obvious (no pun intended).
Joker Doesn't Care?
Joker isn't necessarily the most stable individual. Perhaps his greatest joy is in fighting Batman. These aren't the only instances where it appeared that Joker might know more than he lets on. The big argument could be made that he just doesn't care who Batman is under his mask. The game he's playing is against Batman, now the mild mannered individual underneath. This many not necessarily mean innocents associated with his target are safe as we saw Joker use the fact that he knew where Gordon lived and attacked Barbara to get to him. Why wouldn't Joker do the same to anyone close to Batman?
It may not make sense but when we're talking about the Joker and his reasons for doing what he does, there's just no way to make sense of it all.
Tony Guerrero is the Editor-in-Chief of Comic Vine. You can follow him on Twitter @GManFromHeck. He tries to makes sure certain enemies don't know all of his secrets.