Sen. Frank Lautenberg, D-N.J., the last World War II veteran serving in the Senate, died on Monday following complications from viral pneumonia, CNN notes. He was 89 years old.

Frank Lautenberg died at 4:02 a.m. Monday at New York-Presbyterian Hospital/Weill Cornell, his office announced. Lautenberg had struggled with health problems over the past months causing him to miss several weeks of votes because of what he said was flu and bronchitis.

Frank Lautenberg was not only the longest-serving senator in New Jersey's history, he will be remembered for writing key laws that have saved tens of thousands of lives through his drunk driving and second hand smoke laws. He also wrote legislation that banned those convicted of domestic violence from buying guns. 

Lautenberg first served in the Senate from 1982 to 2001.  He initially retired from the Senate in 2000, after an 18-year run, saying he lacked the motivation to raise money for a fourth term. But in 2002, New Jersey Democrats convinced him to run for the Senate seat held by Democrat Robert Torricelli, who abandoned his bid because he was facing federal corruption charges.

New Jersey Republican Gov. Chris Christie will now appoint a replacement, likely giving New Jersey its first Republican in the Senate since Clifford Case in 1979.

President Obama sent his condolences to the family and called Lautenberg "a proud New Jerseyan who lived America's promise as a citizen, and fought to keep that promise alive as a senator."