Senator Frank Lautenberg, D-N.J. died Monday at age 89. The oldest member of the United States Senate, Lautenberg had represented New Jersey as a Democrat since 1982, except for a short-lived retirement in 2000.

The cause of Lautenberg's death is said to be viral pneumonia. Lautenberg had been suffering from "muscle weakness and fatigue" earlier this year, according to a statement from his office that explained his recent lack of travel. Lautenberg was set to retire again at the close of his term in 2014.

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Frank R. Lautenberg was born in 1924 in Paterson in northern New Jersey to Jewish immigrants from Eastern Europe. His father died while Lautenberg was in his late teens.

Lautenberg later served in the United States Army Signal Corps from 1942 to 1946, during World War II. After the war, he co-founded the payroll company ADP, or Automatic Data Processing. However, in 1982, he decided to leave the private sector and run for the United States Senate.

Lautenberg is credited with being instrumental in the bill that required states to set their drinking age at 21 or incur transportation funding-related penalties.

In 2000, Sen. Frank Lautenberg decided to retire from his career in the Senate, and was replaced by then-future Gov. Jon S. Corzine, D-N.J. However, public demand for Lautenberg's return led him to run against then-Sen. Robert Torricelli, D-N.J. in 2002.

Lautenberg was known to be one of the more liberal Democrats on Capitol Hill. The pro-choice, pro-gun-control Senator was recently honored with a major transportation hub in Secaucus, N.J., being renamed for him. The Secaucus Junction transfer station, just across the Hudson River from Manhattan, now bears his name.

New Jersey Governor Christopher J. Christie, a Republican, will now be called on to appoint a temporary replacement for Lautenberg in the Senate. Christie will likely choose a fellow Republican, who will be in office at least until a special election is held, likely later this year. That Senator will then face another election themselves, if they so choose, at the close of Lautenberg's full term in 2014.

Until the time of Lautenberg's death, Mayor Cory Booker, D-Newark, was seen as a possible Democrat frontrunner to replace Lautenberg in 2014. 79-year-old Sen. Dianne Feinstein, D-Calif. replaces Lautenberg as the Senate's oldest member.