Nearly 50 years after Frank Serpico exposed endemic corruption in the New York City Police Department, his name still divides people.

For some, especially those on the left, Serpico is a whistleblower — a brave loner who took on a sinister system. For law-and-order types and many an ex-cop, he’s a rat who, for the sake of “a few bad apples,” betrayed the men and women who risked their lives protecting New Yorkers from the urban chaos of the ’60s and ’70s. And for film buffs, he’s the inspiration for “Serpico,” Sidney Lumet’s hard-edged 1973 movie that made Al Pacino a star.