She stars as Lagertha Lothbrok in Vikings, one of TV's fiercest female characters, but Katheryn Winnick is totally fearless in real life.

Playing one of the period drama's lead characters, the 37-year-old Canadian actress is making a name for herself in Hollywood as "one of the sexiest and most successful women to grace television screens in quite a while."

But the tagline doesn't sit too comfortably with Winnick, who has made the rare transition from taekwondo instructor to the actress.

"I don't really think about it," she told news.com.au, "I just do my job, and I love doing it, but it's very sweet [of fans to say]."

Winnick's portrayal of Ragnar Lothbrok's first wife, Lagertha, a Viking, shieldmaiden, warrior, and mother, is inspiring and empowering. Her character has contributed to the History Channel, shifting away from being a very male-dominated network.

What fans might not know about Winnick is that she has an insane skill set for martial arts and self-defense. In fact, that might even be an understatement.

Starting martial arts at the age of seven, the self-confessed tomboy received her first black belt at 13. She then opened her first martial arts school at 16 and owned another two by the time she was 21.

Winnick currently holds a third-degree Black Belt in taekwondo and a second-degree Black Belt in Karate. She's also a licensed bodyguard and believes it's essential for women to know how to protect themselves.

"I think every woman has to learn how to defend themselves for sure, and if you can protect your body and have confidence in your body, then you'd be able to defend yourself in any situation. It gives you the power and confidence has to start within yourself."

Ironically, Winnick's impressive training hasn't been all that useful on the Vikings' set, as she had to learn how they fought in the Dark Ages, including wielding a sword.

"I've trained martial arts for many years, it gave me a sense of her [Lagertha's] spirit and her strong will, but taekwondo and Karate is an art form using both hands and feet ... and our style of fighting on the show was very raw and real, versus doing a roundhouse kick," she explained.

Winnick, who speaks five languages (Ukrainian, Russian, French, Italian, and English), said the real challenge had been learning to talk to Old Norse. But, now that they are filming season four, the accent has finally become second nature.

On the show's global success and her own subsequent fame, Winnick said the first three seasons had been one incredible ride.