Arlen Specter (born February 12, 1930) is the senior United States Senator from Pennsylvania and a member of the Democratic Party. Specter was a member of the Democratic Party until 1965, when he enlisted as a Republican in order to challenge the Democratic district attorney of Philadelphia. Elected to the Senate in 1980, Senator Specter staked out a spot in the political center. He has conservative views on crime, gun control and national security, voting to confirm John Roberts and Samuel Alito during President George W. Bush's second term; at the same time, he holds liberal views on abortion rights, immigration, and the environment. In April 2006, he was selected by Time as one of America's Ten best Senators.

On April 28, 2009, Specter announced that, after 44 years as an elected Republican, he was returning to the Democratic Party, citing that he was increasingly "at odds with the (current) Republican philosophy and indicated that polling showed that it would be difficult for him to win the 2010 Republican senatorial primary against Pat Toomey."

Arlen Specter was treated for Hodgkin's lymphoma in 2005 and 2008. He is currently in remission.