One of the time-tested ingredients of a good kdrama is having someone to hate and "Gu Family Book" certainly has a despicable villain. The evil nobleman Jo Kwan Woong has such an extensive list of crimes that viewers long for retribution. He destroys innocent families, ruins the lives of young women and tries to defeat the drama's hero Choi Kang Chi at every turn. Every time you see him, you just want someone to take him out. So, it comes as something of a surprise to find that Lee Sung Jae, the actor who plays him, is really a nice guy and that he has a wicked sense of humor.

Lee Sung Jae is careful to protect his private life, but people who know him seem to think he's fun to be around. When Lee Seung Gi, who plays Choi Kang Chi, was asked who keeps the mood up on set, he first said, "I think it's me."

But he also gave a shout out to his onscreen archenemy.

"Lee Sung Jae is an expert at controlling the mood on set with his humor," said Lee Seung Gi.

Lee Sung Jae has also demonstrated his humor on the MBC "Radio Star" show, making wry comments about guests. He told actor Ryu Soo Young that his looks were "cheesy" and then complimented singer-actor Seo In Guk in a backhanded way for his "rough style" that women found appealing. Later Seo In Guk said that the actor had in fact told him he looked "like a gremlin."

Lee Sung Jae responded by saying that Seo In Guk's looks tended to grow on you. "He's cuter the more you see him," said Lee Sung Jae. "And he's very genuine. "Last time I saw him sleeping I was inspired to give him a kiss."

If you've never seen Lee Sung Jae act in anything before, you might think he specializes in playing villains but his fans actually prefer him in romantic comedies.

He launched his career with a romantic film, "Art Museum By The Zoo" and starred in "Ghost In Love" with Kim Hee Sun. His most popular romantic comedy may have been "Lawyers of the Great Republic of Korea" in 2008. He has had some experience playing bad guys as he did play a villain in the film "Public Enemy."

And his wicked portrayal in "Gu Family Book" may have inspired Lee Seung Gi. After the drama's filming began, the young actor said that some day he would like to try his hand at playing a villain too.