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U.S. Sen. Frank Lautenberg, who grew up poor and became a multimillionaire New Jersey businessman and the Senate’s oldest member, died Monday at age 89.

He died due to complications from viral pneumonia at 4:02 a.m. at NewYork-Presbyterian Hospital/Weill Cornell.

His New Jersey colleague, Sen. Robert Menendez, also a Democrat, praised Lautenberg for his rise from a poor home to affluence and success in business. Sen. Marco Rubio, a Florida Republican, recalled how Lautenberg had been generous with advice and support when he was new in Washington D.C.

Lautenberg had health problems in recent years. A bout with the flu caused him to miss the Senate's Jan. 1, 2013 vote to avoid the fiscal cliff of rising taxes and falling government spending.

He was a champion for working class citizens, especially on issues important to the African American and Latino communities.

— Cid Wilson, New Jersey businessman and civil rights activist

Lautenberg, a member of the Senate Democratic Hispanic Task Force, was a liberal who was called out of retirement for a second tour of duty in Congress. Lautenberg was a long-time leader on environmental protection, transportation and protecting public health.

In a state with one of the largest Latino populations in the nation, Lautenberg was a strong supporter of comprehensive immigration reform, as well as stand-alone measures expanding guest worker programs and allowing undocumented immigrants to participate in the Social Security program. He voted against bills making English the official language of government business and prohibiting documents from being in foreign languages.

Lautenberg often spoke of his affinity with immigrants, noting that he was the son of Polish and Russian nationals, and that he grew up in Paterson, a long-time gateway in northern New Jersey for newcomers from different corners of the world.

Menendez hailed Lautenberg’s personal achievements in a statement.

“His story was an American story. He was a man who joined two of his boyhood friends to found a successful business. He did well, and gave something back and New Jersey loved and admired him for what he did for this nation, what he did to help them build a better life for themselves and their families.”

Rubio recalled how Lautenberg had been a source of comfort when he started in the Senate.

"My wife Jeanette and I will always remember Frank for his kindness and generosity," Rubio said in a statement. "As we settled into life in the Senate, Frank and his wife Bonnie were always incredibly supportive and helpful with their advice and guidance. They helped make our transition easier, and we will always be grateful to them."

Last fall, Lautenberg co-sponsored a resolution with Menendez in honor of Hispanic Heritage Month.

Lautenberg issued a statement marking the month that said: “Across every profession and in every corner of our nation, Hispanic Americans play an integral role in American life. Latino entrepreneurs and educators, entertainers and public servants, scientists and service members—to name just a few—have a positive impact in New Jersey and our country.”

“I stand united with the Latino community, and remain committed to making sure their voices are heard on Capitol Hill.”

Lautenberg was diagnosed in 2010 with lymphoma of the stomach and underwent chemotherapy for the next few months.

He was principal sponsor of a law banning smoking on domestic airline flights.

In February, Lautenberg said he would not seek a sixth term. He was up for re-election in 2014.

Gov. Chris Christie, a Republican, now must appoint a replacement for Lautenberg.

Even before the senator made known his intention not to run again, several people, including Newark Mayor Corey Booker, a Democrat, and Republicans such as state Assembly Minority Leader Jon Bramnick of Westfield, state Sen. Joe Kyrillos of Monmouth County and Lt. Gov. Kim Guadagno had said they were considering running for the seat.

Geraldo Rivera, the host of a Fox News show and Fox News Latino contributor, said earlier this year that he was "seriously contemplating running" for the U.S. Senate in his home state of New Jersey.

He said that he would run as a Republican.

Lautenberg was the last remaining World War II veteran serving in the Senate.

Cid Wilson, a Dominican-American who serves on the boards of several of the nation's leading Latino and African-American civil rights organizations, said: "He was my U.S. Senator since I was a young child. He was a champion for working class citizens, especially on issues important to the African American and Latino communities."

"I had the wonderful opportunity to work with Senator Lautenberg in my local, state, and national capacities over many years and will cherish the times I spent with Senator Lautenberg," Wilson said. "When we needed a champion in the U.S. Senate for civil rights, immigrant rights, education rights, and voting rights, there was no greater friend to the community than Senator Frank Lautenberg."

Lautenberg is survived by his wife, Bonnie Englebardt Lautenberg; six children and their spouses, Ellen Lautenberg and Doug Hendel, Nan and Joe Morgart, Josh and Christina Lautenberg, Lisa and Doug Birer, Danielle Englebardt and Stuart Katzoff, Lara Englebardt Metz and Corey Metz; and 13 grandchildren.

The Associated Press contributed to this report.