Arlen Specter, a gruff, independent-minded moderate who spent three decades in the U.S. Senate but was spurned by Pennsylvania voters after switching in 2009 from Republican to Democrat, died on Sunday of cancer, his family said. He was 82.

Specter had announced in August a recurrence of non-Hodgkin lymphoma, cancer of the lymphatic system. His son Shanin Specter confirmed his death.

Resilient, smart and aggressive, the former prosecutor frequently riled conservatives and liberals on his way to becoming Pennsylvania’s longest-serving U.S. senator. He was elected to five six-year terms starting in 1980. He left the Republican Party because he said it had become too conservative.

Specter steered a moderate course during an era when the two major U.S. political parties became increasingly polarized, and often broke with his party. His sometimes testy demeanor and opportunistic maneuvering earned him monikers like “Snarlin’ Arlen” and “Specter the Defector.”

In 2009, Specter left the Republican Party after 44 years when he concluded he could not win his party’s primary in Pennsylvania in 2010 against a conservative challenger. But his bid for re-election in 2010 ended in failure when he was beaten by a liberal challenger for the Democratic nomination. Read more in NBC.