Oscars 2012: Brad Pitt, George Clooney Most Charitable Oscar Nominees

In just a few short hours, Oscar hopefuls will descend on the premiere awards stage to vie for the career-defining trophy.

But for some of the nominees, getting recognition for stellar acting performances isnt the only mark of great achievement.

Making a difference in the world by stepping up for those in desperate need of help is a role these thespians play year round.

Who made it to our list of the the top seven nominees making the greatest impact? Click through our slideshow to find out.

SLIDESHOW:

It's hard to imagine Melissa McCarthy doing anything but cracking us up. But the "Bridesmaids" star demonstrated just how committed she also is to fighting cancer when she attended a Livestrong event in January. "Everyone knows the name, knows what it's about," McCarthy told the "Insider." "It still needs money, you still need to donate, you still need to be aware. The fight is still on."
It's hard to imagine Melissa McCarthy doing anything but cracking us up. But the "Bridesmaids" star demonstrated just how committed she also is to fighting cancer when she attended a Livestrong! event i n January. "Everyone knows the name, knows what it's about," McCarthy told the "Insider." "It still needs money, you still need to donate, you still need to be aware. The fight is still on."
It's hard to imagine Melissa McCarthy doing anything but cracking us up. But the "Bridesmaids" star demonstrated just how committed she also is to fighting cancer when she attended a Livestrong event in January. "Everyone knows the name, knows what it's about," McCarthy told the "Insider." "It still needs money, you still need to donate, you still need to be aware. The fight is still on."

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