It was Joe Chill, he's confusing the mugger in the reproduced panels from Detective Comics #33 (1939) that were featured in Batman #1 (1940) for the Joker because the Joker was introduced in Batman #1 (1940). The mugger and the Joker are not the same person. The mugger was just that until he was named in Batman #47 (1948).:batman: I believe the first significant murder that the Joker did in Batman's life was Jason Todd but I could be wrong on that though.
The Joker's done alot of shit.
He effectively, ended Dick Grayson's role as Robin in Batman #408 with a story titled, "Did Robin Die Tonight?". While the Joker only appears for the first quarter of this comic book, he changes the future Batman history dramatically by shooting Robin (Dick Grayson) and sending him down the side of a building to his death! As some of us comic book fans are well aware of, Dick survives and becomes Nightwing, but the Batman legend has never been the same since.
Yeah, Joker killed Jason Todd.
Joker also crippled Barbara Gordon (aka Batgirl) in the popular
The Killing Joke.
And he's also more recently murdered Jim Gordon's wife during the "No Man's Land" arc.
I'm not sure why METAL HEAD insist's that the Joker murdered Bruce Wayne's parents, but again that's definately NOT the case in any DC comics I've read. However, the Joker's first name has been referred to numerous times as "Jack". And the "Jack Napier" name did crossover into the
Batman the Animated Series as well.
But as the murderer of Bruce's parents? Nope.
Again, that was Joe Chill.
And if you REALLY want a quick rundown on Joe Chill, it goes like this;
Joe Chill: Revealed as the mugger and murderer of Bruce Wayne's parents during the 1940's.
Following Frank Miller's "Year One/Year Two" arcs, Joe Chill STILL was the killer. Only he was killed off by a villain called, "The Reaper" rather than by other criminals like in the 1940's version.
Then came "Zero Hour" in the mid 1990's. Which wiped out Joe Chill from Batman's history, and which resulted in Batman never having known who killed his parents.
Ultimately, a mega DC Comics event called, "Infinite Crisis" re-instated Joe Chill back as the murderer of Bruce Wayne's parents, and even went as far as illustrating that he was caught by authorities shortly afterwards. Which of course, was done to sync up with what we saw in
Batman Begins.
Case Closed.