SUMMARY: Sirius Black died a debatable death. Most people point the finger at Kreacher, his unwilling house-elf, but I don't think the creature is all to blame. True, he did betray Sirius' great love of Harry, but perhaps had Sirius shown the elf more respect Kreacher wouldn't have done it. In this quibble, I am going to delve deeper into what happened and how it all went wrong.
Sirius Black is portrayed half hero, half tyrant. Harry has only ever seen the heroic streak, but Snape the monster side alone. Pettigrew also gets a terrible blast of his temper in the Prisoner of Azkaban, and Mrs Weasley occasionally gets a dousing. Sirius is also reckless and would die saving or refusing to betray his friends, as he did. Sirius doesn't believe in the persecution of the innocent, and despises the "purebloods only" idea. Through this, he grows to hate his pureblooded parents, who thought Voldemort was fine, and his brother Regulus. Sirius also detested Slytherins, the first Black to be a Gryffindor, truly different to his forefathers. He could be touchy, at the mentions of his cousins the Malfoys and Lestranges especially, despite his good heart underneath. However, he also believes some spots don't come off and are unforgivable.
Kreacher, on the other hand, is the opposite. He can only recall those he once worshipped and their grudges, Mrs Black, Mr Black and Regulus predominantly. He thinks, as those he favoured in the past did, that purebloods only was correct. But when Regulus dies at some Death Eater's hands, Kreacher changes his opinion of Voldemort. But, despite the women being Death Eaters themselves, Kreacher tells Bellatrix and Narcissa of Sirius' love of Harry without turning a hair. This is because he operates for those who are kind to him (and he doesn't have enough hair anyway); he obeys those who tolerate his weird mutterings and be nice anyway, and he likes those who give him things. Regulus was very nice to him, and Mr and Mrs Black earned Kreacher's respect by "knowing the purity of their blood" (Kreacher's tale, the Deathly Hallows), as Regulus did (and Sirius did not). Kreacher disliked Sirius because Sirius thought differently to his ancient family, and Kreacher had the same views as his masters and mistresses. He couldn't think for himself, and that's where he and Sirius were so very different.
Kreacher was mistreated by Sirius for many years because of this. Kreacher used words to retaliate, though Sirius didn't care. He was convinced that, evil and accursed the creature might be, he was harmless. But Kreacher showed Sirius he was wrong. Thanks to the ugly elf, Narcissa Malfoy and Bellatrix Lestrange wheedled priceless information from Kreacher, they told their master and Voldemort planted a false image in Harry's mind. This led to the Ministry fiasco, (the Ministry of Magic, the Order of the Phoenix), the smashing of the prophecy and the imprisonment of Lucius Malfoy in Azkaban. When Sirius sped over to the rescue, accompanied by Lupin, Mad-Eye, Tonks and Kingsley Shacklebolt, duelled his dear cousin Bellatrix, gave that last exhilarated laugh and toppled through the veil, the laugh was on him. When it was added up that Kreacher had played a crucial part in this, I saw him in a different light. I had never seen Kreacher that badly before, though I didn't like his words with Hermione. I saw him differently: a brainless, impolite, rude elf who had betrayed Sirius to Voldemort. It was as though Kreacher himself was veiled, his real evilness masked, and he whipped the veil off by giving Sirius away. He did improve once he got the locket (Kreacher's tale, the Deathly Hallows), but that was bribery and a despicable way of swapping sides.
Kreacher's bad points were all outlined and all flourished when Sirius died, but he was not all to blame. We cannot forget the manner in which Sirius treated Kreacher. The two hated each other, ever since Sirius had argued with and deserted his family. Kreacher clearly hadn't forgotten this, and held it against his master - but wasn't counting on Sirius returning, either.
Kreacher was quite rude to Sirius - but Sirius was no angel to Kreacher either. Sirius, as I have indicated already, was not fond of the house-elf because it echoed the Black's opinions relentlessly. Sirius couldn't stand anyone harping on as his late family did, and Kreacher devoted his later life to doing it. Sirius was harsh and sharp. Kreacher was lowly, worshipping and a version of humble, but was also harsh and sharp.
Sirius should have known, with the house-elf lurking in the headquarters of the Order of the Phoenix, that it should be treated with caution. Sirius should have known that the elf would love to see the back of him, and could resort to anything. Sirius should have learned to tolerate the elf and respect it, but he did not. It was due to Sirius' disrespect, Kreacher's love of the Blacks and Kreacher's hate of the last Black that Sirius was thrust into Death's welcoming arms by the creature he had never appreciated.