actually this batman is basiaclly the same batman:
Miller explained that in Amazing Heroes #102. He seems different in Batman: Year One because he was very young and inexperienced. But as silentflute points out, it's certainly the same person.
"The 55-year-old Batman of Dark Knight is very different from the 25-year-old Batman of 'Batman: Year One.'" Miller explains. "He's very young, very enthusiastic. He may be Batman at his most joyful. He's a young man. He's also a Batman who makes a lot of mistakes. He's a young man who charges out thinking he can change the world on his own. He learns that he can't. He finds out that the abilities of one man are limited, even an extraordinary man like him. No matter how skilled you are, if the numbers are against you, you need a psychological advantage, which is what the bat costume gives him. Even as he learns the bat-symbolism to scare people, he finds himself very quickly outnumbered."
In Wizard #162, Jim Lee and Dan DiDio explained about Batman in All-Star Batman & Robin: "It's Batman in his prime!" Lee says excitedly. "Batman is more of an S.O.B. than in Batman: Year One. I think he's tougher; more of a force of nature. Don't stand in his way because nothing is going to stop him." "Batman has also never experienced the lose of a partner (as Batman in Dark Knight Returns had)," DiDio adds. "He's in the process of training someone to stand by his side while he perfects his craft."
Miller himself explained about Batman in All-Star Batman & Robin to Newarama: "He is a dick. He dresses up like a bat, and throws people through windows nightly. His only human contact is with a cranky butler. Now he’s got a twelve year old boy on his hands, and he’s trying to play daddy, and it ain’t going to work. Of course he’s a dick. He explains it to Alfred in the story, saying, “I’m a young man, but I won’t always be young, and the mission has to continue.” Robin is his apprentice. He's training his replacement. That's the life he intends for Robin. Of course Alfred's reaction is, "I'm dyspeptic!" and is horrified that Bruce would do such a thing, and even, if he did something like that, admit it out loud. Alfred already has to deal with this nutcase as a boss, and now he has to worry about a kid as well. Batman had been watching Dick Grayson because he was the most talented kid he'd seen yet. I felt that somebody finally had to explain why he would bring a kid into his world. Bruce was going to wait, as he puts it, “Until the kid was old enough to shave.” He was planning on taking him under his wing in maybe another six years, but instead, he has to do it when the kid is still too young for the job. It was the murder of Dick Grayson's parents that forced his hand. There's always banter back and forth, where Robin thinks that a lot of the stuff Batman does is old fashioned and weird.
I love the "Boy Wonder" line, before he was turned into the Teen Wonder, and almost a "Grim Robin." But I just love the idea of a young Robin. That's why I created Carrie Kelley in Dark Knight - I just loved the contrast between this stocky, tough, dark adult, and a colorful little pixie running around.
Also – if you're older than 12, are you going to come up with that costume? Do you think Bruce would? Robin creates "Robin," essentially. Bruce hadn't thought this thing through enough, given that he was somewhat "forced" to take Robin in before he – both Bruce, and Dick – were ready. Handling a kid? That's kind of outside his purview – somewhere outside of what he trained himself for. So he's struggling with the whole thing."
In Comics Interview #31, Miller explained about Batman in Batman: Dark Knight Returns:
"During the ten years that he isn't Batman that precede this series (after Jason Todd's death), he's a dead man," explains Miller. "Bruce Wayne goes through the motions but there's no one home. In the beginning of the series in fact, Bruce refers to Batman as "him." During the ten years that he hasn't been Batman he's gotten into racing cars. But he was born to be Batman, and whatever Bruce Wayne might have been is completely irrelevant. Bruce Wayne is Batman's host body. Bruce Wayne died when his parents go blown away. He really loves fighting crime. He's fighting what is in his mind a holy war. In my series I put forth the idea that he was always going to be Batman, that his parents murder was as inevitable as him putting the costume on. In fact, I have an incident earlier in his life that foreshadows what's going to happen to him (when he falls down into the cave as a child and meets the bats). Fate.
Batman's methods can't be nice. Much of what he does to criminals is staged like a horror movie. He's the hero who acts like a villain - the epitome of the Dionysian hero, just as Superman - the Appollonian hero. In Christian terms, Batman commits evil to fight evil. And the whole problem with Batman is that he makes no compromises along the way. When he comes out of retirement he acts exactly as he did before. Except he's a bit less patient now because he's only got a certain amount of time left. The central conflict is the world versus Batman.
I stress that Superman and Batman are enemies, and that Superman and Batman have been enemies for decades. They've never liked each other. Batman has tremendous contempt for Superman because he's such a "good boy," because he takes orders, from the President, among other people. Superman is something of a federal agent. And Superman, frankly, is scared of Batman. Because Batman represents to a certain extent, his own dark side. Which Superman doesn't want to look at. They imply completely different points of view. Superman implies a benevolent world - Batman implies a malevolent world. I cannot see two personalities like that getting along, acting friendly.
Originally, my feeling was much like many other people's - I had always thought that Robin was a real pain-in-the-ass, but I now realize what a brilliant creation it was, because it really does give a human context to Batman's character. If Batman is done properly, he's such a powerhouse that he needs a restraining figure - and just a human being to be with him, especially a brightly-colored child, as perverse an idea as it is that a grown man would drag a child into the bullets!"
Miller explained to Comic Book Resources about Batman in DK2:
"In the first Dark Knight, Bruce was a very self destructive, tortured man," explains Miller. "He was endlessly angry. When this story begins, three years have passed and he looks younger than he did in the first Dark Knight. He is strangely happy and at peace. He is a much more powerful figure and he has been tested. Every hero has to be tested, that's how they're defined. Batman's trained all his troops underground and is finally reemerging to bring back the glory boys to save the day."
proof Batman laughing in Dark Knight Returns, Batman year one and All Star Batman and Robin,Joker's poisoning of the water supply, Jim Gordon's affair with Sarah Essen, whom he is clearly still in love with, while still being married to Barbara, Jim beating up detective Flass, the inclusion of the Joker's henchwoman, Bruno from Dark Knight Returns
links the continuity of All-Star Batman
, as well.