Klaus is a vampire and one of The Originals and their leader. He is mentioned by Rose to Stefan. He is the main antagonist of the second chapter of Season 2 and possibly the third chapter and the third season as well.
Klaus has only been mentioned on the show, but has wanted to break The Sun and Moon curse. The only people that has been known to see him is Elijah and Katherine's family. He was a nobleman in late 15th century England where he met Katherine.
After Katherine escaped and was turned into a vampire, Klaus traveled to Bulgaria where he killed her family as revenge, leaving her alive so that she would have to live with the guilt. Despite her ruthlessness and the fact that she seems to have lost her humanity, Katherine truly does miss and loved her family as seen in Katerina when she was seen crying in the tomb over her family's history book.
Klaus possesses all the powers and weaknesses of a vampire. Due to being an original and their leader, he is known to be the oldest and most powerful vampire in the world but likely not the first vampire in existence. He is more powerful than the rest of The Originals.
In the Books, Klaus was the one who transformed Katherine into a vampire, on the series, it ended up being Rose who played the part, and Klaus and Katherine's backstories have been completely changed from the books.
Who should play Klaus?
I've already suggested that Alexander Skarsgard (aka Eric Northman of True Blood) should play Klaus. He's Sweddish so he would fit the description. Many other people around the web picture him as Klaus, which surprised me. I'm not the only one! But I'm afraid that's not gonna happen =(
So these are the top choices around the web... who would you pick? one of these? another one?