Arlen Specter: Influential Senator for the Democrats and Republicans

Ronald Reagan raises Specter's hand at a fund-raising party for Specter in 1980 (AP)

Maverick" is an overworked word in the political lexicon, but it applies perfectly to Arlen Specter, a giant of the US Senate, a moderate in views if not in manner, who over his three decades on Capitol Hill career would constantly infuriate liberals and conservatives in equal measure. He began his career in public life in 1965 by running – and winning – as a registered Democrat on the Republican ticket for district attorney for the city of Philadelphia. He ended it, to all intents and purposes, in 2009 when, his Pennsylvania seat under dire threat from a far-right challenger, he switched back from the Republicans to the Democrats. This time he was less successful, losing in the Democratic primary to a challenger from the left.

In between Specter made his mark as one of the most powerful minds in the Senate, an influential voice in some of the most contentious issues of his time, from abortion to economic policy. His most influential perch was the Senate Judiciary committee, where his aggressive questioning style, honed as a public prosecutor, played a pivotal role in two of the most controversial Supreme Court nominations of recent times.

In 1987 he helped prevent confirmation of the conservative judge and legal scholar Robert Bork, who had been nominated by Ronald Reagan, in the process enraging many in his own Republican party. Four years later he made amends with his blistering attacks on Anita Hill, whose claims of sexual harassment threatened to derail the nomination of Clarence Thomas, nominated by Reagan's successor, George HW Bush.

At one point in he accused Hill of "flat-out perjury" in her testimony. Thomas was eventually confirmed, but such was the venom of womens' groups that the affair almost cost him re-election to the Senate in 1992. The man himself was typically unrepentant: "I did not ask her one unprofessional question," he told The New York Times in 2004.

The son of Jewish immigrants from Russia, Specter spent his childhood in Kansas. The family's circumstances were modest; his father started out as a peddler before running a scrap metal business during the Second World War in the small town of Russell – birthplace, as it happened, of Robert Dole, the Republican leader in the Senate for much of the time Specter served there.

After the war the Specter family moved to Philadelphia and, armed with a law degree from Yale, the son won a job in the city district attorney's office. His, hard-hitting forensic style was quickly noticed. In 1964 Specter was taken on as a junior counsel for the Warren Commission set up to investigate the assassination of President Kennedy, where he was originator of the "single-bullet" theory – embraced by the Commission – that the same shot, fired by a single gunman, hit both Kennedy and the Texas governor John Connally, who was travelling in the president's limousine.

The following year, Specter was elected Philadelphia's DA, a job that is often springboard for a successful political career. In 1980, by now a registered Republican, he won the Senate seat vacated by Richard Schweiker, and soon emerged as a power on the Judiciary Committee.

But although Specter was a centrist – he was an early supporter of stem cell research, and a fervent defender of a woman's right to an abortion, and in 2009 was one of only three Republican Senators to back President Obama's $780bn stimulus bill – he was not one of the meek and gentle variety. Never a person to suffer fools, he often came across as arrogant and brusque. "Snarlin' Arlen" was his nickname on Capitol Hill, and his inability to practice touchy-feely politics, and the mistrust he inspired on both left and right, doomed what scant chances he had in his lone presidential bid, for the 1966 Republican nomination. Specter dropped out before a single primary vote was cast and endorsed Dole, who became the party's nominee.

As the Republicans moved right, Specter became steadily more uncomfortable and isolated. As early as 1995 he was describing Christian conservatives as an extremist fringe, and after his support for the 2009 stimulus his position became untenable.

Facing defeat in his 2010 Republican primary Specter switched sides, briefly providing Obama a filibuster-proof Senate majority of 60 in the 100-seat chamber. Unfortunately, Democratic primary voters preferred the liberal Joe Sestak, and Specter's nine political lives were finally exhausted. He died of cancer, first diagnosed in 2005.

Arlen Specter, politician: born Wichita, Kansas 12 February 1930; District Attorney, Philadelphia 1966-1974; US Senator for Pennsylvania 1981-2011; married 1953 Joan Levy (two sons); died Philadelphia, Pennsylvania 14 October 2012.