Leonardo DiCaprio turns 40: From humble beginnings to Hollywood star

Leonardo DiCaprio celebrates his 40th birthday Tuesday and the seasoned actor looks a lot different than the fresh-faced teen who made his first mark on Hollywood starring in "Growing Pains" back in 1991.

Critically-acclaimed roles in films like "What's Eating Gilbert Grape" and "The Basketball Diaries" led to blockbuster success with hits like "Titanic" in the 1990s. By 2002 he began working with famous director Martin Scorsese on "Gangs of New York," and the duo have continued their partnership since with big hits like "The Departed" and 2013's "The Wolf of Wall Street."

DiCaprio expanded his career outside of Hollywood as well, becoming a Messenger of Peace for the United Nations earlier this year. But his U.N. gig wasn't his first foray into politics, having campaigned for presidential candidate John Kerry back in 2004.

But while he's become a Hollywood A-lister, one prize still eludes Leo: an Oscar. He was first nominated for his supporting role in "What's Eating Gilbert Grape" back in 1994, but he still hasn't won the coveted award.

Check out Leo in some of his most famous roles (and some you might have forgotten) in the gallery below.

Watch a 16-Year-Old Leo flub his first ET interview: