Everyone loves Dobby, but you might become a little more sympathetic to Kreacher with this new theory.
In a Reddit thread titled "Why Kreacher the elf is such a prick," people believe Kreacher acted terribly because of the Salazar Slytherin locket horcrux. He lived with the locket in the same house for so many years and ultimately could only think negative thoughts and ideas. A similar effect happened to Ron Weasley in the books: when Ron wore the same locket, he became angry and resentful.
However, that's where people's opinions begin to differ. Ron actually wore the locket, which most likely led to his negative emotions, whereas Kreacher was just existing in the same house with it. Many users, like Do_The_Africa_Face below, believe Kreacher acted so terribly because he was treated so badly.
"His behavior may have been amplified by the horcrux, but Kreacher was not treated well by his left over masters and had a fierce sense of stubborn 'pride' instilled in him by long service to a family well connected to the dark arts."
Whether you believe it or not, you can't deny that there is plenty of evidence that points to similar characters once thought of as terrible, like Salazar Slytherin, actually being thoughtful people.