Justin Bieber - Justin Bieber: 'I'm Still The Underdog'

The Baby hitmaker has become a household name at the tender age of 18, but he insists nasty comments from detractors inspire him to always try his best as he attempts to broaden his target audience from kids to adults.

During an upcoming U.S. TV interview with NBC correspondent Ryan Seacrest, which airs on Thursday (13Sep12), he says, "It gives me and my fans something to do and to strive for next.

"I feel like, in some ways, I am the underdog. Because it's like there's... there's people that don't believe that... I can make the transition from being a teen pop star to an adult. So I think that, yeah, definitely."

Bieber admits he's keen to prove he's more than just a pop heartthrob and his new album Believe is his most mature sound to date.

He adds, "I feel like I just don't want to be another teen heartthrob, 'cause... I just think that that just annoys me. To think that that's what people will think of me, I just want to prove people wrong...

"I think Believe has really showcased what I'm capable of, especially becoming an 18 year old and becoming an adult. And hearing older people say, 'Wow, this new album's great. Like I didn't know that was Justin Bieber.' Or, you know, 'Wow, like I never used to listen to Justin Bieber's music, and now I like his music.' Or, 'This, 'As Long As You Love Me,' that's Justin Bieber singing?' I like those reactions, because I feel like they're judging me based on my music and not based on, you know, a flick of my hair."

And the singer claims the ultimate goal would be to land his very own Grammy Award.

He says, "That's something that I've always - when I was little, like, 'Oh, my God, like, what if I won a Grammy? That would be crazy.' So that's one of the things that I'm still striving for."