If you watched 3rd Rock From the Sun growing up, then you know that Joseph Gordon-Levitt wasn't always the hunky heartthrob [1] he is now. When he landed his first major TV role as Tommy Solomon (an alien living as a young boy) in 1996 at the age of 15, JGL was a cute-as-a-button mop-haired boy who soon graced the cover of countless tween magazines. Over the years, the actor maintained his boyish charm, and it wasn't until he appeared in 500 Days of Summer in 2009 that the world realised, "Damn, Joseph Gordon-Levitt is hot!" Check out the gallery to see JGL's adorably awkward transition from boy to man [2] over the years.

2001

An adorably serious 20-year-old Joseph Gordon-Levitt (yes, believe it or not, he's 20 here) attended the E! Party during the 2001 Sundance Film Festival in Park City, UT.

2001

During 2001's Sundance Film Festival, he also had his portrait taken for Manic, which he starred in opposite his future 500 Days of Summer costar Zooey Deschanel [3].

2002

He donned a sweet pair of glasses for the Treasure Planet premiere at the Cinerama Dome in Hollywood in 2002.

2002

He even looked cute in his puffy red jacket and messenger bag when he arrived for the 25th Hour world premiere at the Ziegfeld Theatre in New York.

2003

Not much had changed by the premiere of XX/XY at the 8th Annual Gen Art Film Festival's Closing Night Gala at Loews Astor Plaza in New York, except the colour of his puffy jacket.

2003

He was his usual charming self at the New York premiere of Manic at Village Cinema #7 in New York, over two years after it was first shown at Sundance in 2001.

2003

For the Amelia Toro Fall 2003 Fashion Show at Avalon Hotel in Beverly Hills, JGL showed up in a sporty varsity jacket.

2004

He grew out his hair (and looked very much like his old 3rd Rock From the Sun character, Tommy) for the Point and Shoot premiere at the 3rd Annual Tribeca Film Festival.

2004

And he completed his nerdy-chic look with a pair of glasses and a backpack for the Thunderbirds screening at the Tribeca Film Festival.

2004

By the time the 2004 Venice Film Festival rolled around, JGL had really blossomed from boy to man (and it only took 23 years to happen).

2004

For the Mysterious Skin premiere at the Venice Film Festival, he wore a tie and everything.

2004

Just look how cute his festival portrait turned out!

2004

At the Silver City party during the Toronto International Film Festival, JGL arrived with his trusty messenger bag and looking way too young to be holding that adult beverage.

2004

But during the Hollywood Foreign Press Association Toronto Film Festival party, he was all smiles and back in a tie and jacket.

2005

For the Brick premiere at the 2005 Sundance Film Festival, his adorable argyle sweater also made a premiere (and his long hair made a comeback).

2005

Seriously, that sweater is everything.

2005

Though he still couldn't find a suit that fit him right by 2005, his sweet smile at the 31st American Film Festival of Deauville made his outfit forgivable.

2006

By the time the Los Angeles Shadowboxer premiere at Arclight Theatre rolled around in 2006, JGL had clipped his hair and was finally starting to look like the actor we now know and love.

2007

Only he could make an arm sling look cool, which he wore along with a smart suit to the Los Angeles premiere of The Lookout at the Egyptian Theatre.

2007

At Remember the Daze (originally titled The Beautiful Ordinary) world premiere at Landmark's Regent Theatre in Westwood, CA, he was looking more manly than ever.

2008

He even showed up with — gasp! — facial hair for the Los Angeles Stop-Loss premiere at the Directors Guild of America in Hollywood.

2008

At Hollywood Life Magazine's 10th Annual Young Hollywood Awards at the Avalon, it seemed as though 27-year-old JGL had finally found a style and a haircut that really worked.

2009

And when 500 Days of Summer premiered during the Sundance Film Festival at Eccles Theatre, Joseph-Gordon Levitt officially had our hearts.