President Barack Obama greets Kennedy Center Honoree Meryl Streep in the Blue Room of the White House, Dec. 4, 2011. Credit: Official White House Photo by Lawrence Jackson

Happy Birthday, Mr. President!

President Barack Obama celebrated his 51st birthday on Saturday in low-key fashion: With a morning round of golf at Andrews Air Force Base and then a day of relaxation at Camp David with wife Michelle and their daughters Sasha and Malia.

Next Sunday, the POTUS will be feted in more public fashion at a bash in his Chicago home that will double a re-election campaign fundraiser, according to the New York Times, that's sure to draw some loyal fans and supporters from Hollywood.

With less than 100 days to go before Election Day, Obama is getting help from a slew celebrities in his bid against Republican Presidential contender Mitt Romney -- with Octavia Spencer, Zach Braff, Donald Faison, Don Cheadle, Zachary Quinto, Justin Long and Blythe Danner recently hosting grassroots events nationwide.

In 2011, Obama hit the mid-century mark with Jennifer Hudson crooning the Happy Birthday song at a star-studded bash; this past May, George Clooney hosted a $40,000-a-plate fundraiser for the POTUS, raising an estimated $15 million.

And then there's Beyonce, who unforgettably celebrated the President's inauguration with her own rendition of Etta James' "At Last" in early 2009. (Barack himself has heaped praise on Beyonce's husband Jay-Z, while Michelle and the girls recently rocked out at a Memorial Day Beyonce concert.)

Who else in Hollywood has hobnobbed with the President? Click through the gallery and find out!