Happy birthday, Justin Bieber! The YouTube sensation turns 21 today. He quickly rose to fame after his manager discovered him through his YouTube videos and his debut album went platinum (so did his hair earlier this year) with seven songs charting on Billboard's Hot 100, the first artist to do so. Since then, the Biebs has won numerous awards, including Artist of the Year, and recently appeared in Calvin Klein's steamy campaign with Lara Stone. The teen heartthrob turned bad boy will be roasted by Comedy Central later this month. In honor of his birthday, take a look back at his standout looks through the years.