John Paul Stevens, appointed to the Supreme Court in 1975, is the oldest member of the current Court and, behind Chief Justice Rehnquist, the second-longest serving. Nominated by Republican President Gerald Ford in the wake of the Watergate scandal to help re-establish public confidence in government, Stevens was widely viewed as a moderate, concerned more with the details of a given case than a broad and predictable judicial philosophy. As the Court moved to the right during the Reagan and Bush administrations, however, Stevens began to ally more often with the liberal bloc. He has voted to uphold Roe v. Wade and a woman's right to abortion, for example, and has resisted the Federalism doctrine that is one of the most notable characteristics of the Rehnquist Court.
As the senior member of the liberal wing, Stevens often controls the assignment of opinions in closely-decided cases. Still, his influence remains uncertain. Many observers point to his quirky and unconventional jurisprudence as a constraint on his ability to lead the Court. They argue that Stevens' individualistic personality keeps him permanently outside the mainstream of the Court and that he lacks the characteristics of a coalition-builder. Nevertheless, in light of the Court's close ideological split and Stevens remarkable intelligence and experience, it would be difficult to discount his role in determining the Court's direction.
above lifted from
http://www.oyez.org/oyez/resource/legal_entity/101/biography