In an almost 40-year career, American actor Ray Liotta has made quite an impression playing cops on the wrong side of the law.

In Unlawful Entry (1992), he becomes obsessed with a married woman; in Cop Land (1997), he is entangled with a group of corrupt officers; and in Narc (2002), he is a detective clashing with the internal affairs department.

Now, in TV drama Shades Of Blue, he plays Lieutenant Matt Wozniak, who heads a tight-knit unit which takes the law into its hands. The team includes detective Harlee Santos (Jennifer Lopez), a single mother whom he looks upon as his own daughter.

But this is no mere retread of his past roles. For one thing, the character he plays is bisexual and kisses his male lover cop in Episode 3.

Speaking to the media over the telephone from Los Angeles, he says: "It was one of the reasons I wanted to play the part, because this bisexual aspect came out of left-field. As an actor, you want to play as many different parts as you can."

On the kissing scene, he says: "I looked at it as an acting exercise. Luckily, it was short and fast and it wasn't French kissing or anything. It was odd, very, very strange and different."

Liotta, 61, says his body of work is far more diverse than simply playing men in blue in shades of grey. In "more than 75 per cent" of his more than 80 movies, he has played good guys, including "two movies with the muppets", he says.

But what people remember are his unnerving turns as the mobster in Goodfellas (1990) and the insane ex-boyfriend in Something Wild (1986), which earned him a nomination for a Golden Globe Award for Best Supporting Actor.

For all the menacing characters he has played, he has been in only one fight in his life. He recalls of that spat when he was in seventh grade: "I think we were arguing about whose cafeteria food was better. It was that silly, it was that stupid of a fight."

He adds: "I think bad guys have a tendency to stand out more than good guys, it's the nature of the beast. There's just something that appeals to people."

It was also why he was approached for the role of Wozniak in Shades Of Blue. He says: "They came at me really hard because Jennifer is not known for these kinds of edgy pieces. They needed someone like me to legitimise the piece because I've played bad guys before in a very real way."

Initially, he had some reservations. As he puts it: "I didn't want to be in the Jennifer Lopez show."

That said, he adds: "She's really good in this, she really is Jenny from the block, there's a really nice edge she has. And now, after having done a season, I can't picture anybody else but Jennifer doing this."

The show, which has received mixed reviews with both its stars being singled out for praise, has been renewed for a second season.

While he continues to seek out good parts, his most important role is being a parent. He says: "I'm a single dad and there's nothing more important than raising a well- adjusted kid. There's no better, bigger, more important job than that."

•Shades Of Blue airs on Universal Channel (StarHub TV Channel 512), every Tuesday at 9pm.