Shabos goy is the term used by orthodox Jews for gentiles who help them with certain tasks they’re forbidden from doing during the Sabbath, such as operating electrical devices.
According to Newsweek’s excellent cover story on Obama’s faith, when he was a state senator in Illinois his roommate was Ira Silverstein, an Orthodox Jew. He peppered Silverstein about questions on Kosher rules:

“On the Sabbath, if I ever needed anything, Barack would always offer,” remembers Silverstein. “Some of the doors are electric, so he would offer to open them… I didn’t expect that.”

UPDATE: Thanks to commenter Manachem Petrushka who points out: “Senator Barack Obama is not fisrt celebrity to have been a ‘Shabbos Goy’ Elvis Presly and Colin Powell offered their serviced to help out religious Jews on the Sabbath.”