Quote from : Harry Potter and the Order of the Phoenix Movie

Kreacher: [to Harry] Nasty brat standing there as bold as brass. Harry Potter, the boy who stopped the Dark Lord. Friend of Mudbloods and blood-traitors alike. If my poor mistress only knew...
Sirius Black: Kreacher! That's enough of your bile. Away with you!
Kreacher: [smiles] Of course Master. Kreacher lives to serve the noble house of Black.