I know, I know, he was kind of responsible for Sirius death as they say in the books, but he had endured years of abuse and horrible treatment. He played a part in getting the locker Horcrux with Regulus. He watched his master die! He was broken. But when Harry, Ron, and Hermione showed up at Grimmauld Place, he showed them kindness. And just think, who was it that lead the Hogwarts house elf's in the Battle of Hogwarts?