I have seen the season The Originals and in the end Klaus Michelson killed his father. I can't understand why he did this.
Because he needed "Viking ash" to make the weapon to kill Dahlia. Where else they can get Viking ash? Do they have enough time to search?
So Klause did what he felt right, burning a Viking to get the ash and first he is, not his real father and second whole life he tried to kill Klause so it was not so tough decision.