Former Pennsylvania Senator Arlen Specter — a mainstay of American politics for three decades — died of cancer Sunday morning at the age of 82.
Specter — the longest-serving U.S. senator in Pennsylvania history — served as a Republican from 1980 until he switched parties in 2009.
His loss in Pennsylvania’s Democratic primary the next year marked the end to a unique — and often contentious — political career.
In 1964, Specter made his first mark on the national stage with his contribution to the Warren Commission, investigating the assassination of President John F. Kennedy.
A young Philadelphia prosecutor at the time, Specter was the man behind the “single-bullet” theory — the idea that a single shooter both wounded Texas Gov. John Connally and killed the president with one shot.
To hear more about Specter’s life, check out the video above.