Nelson Wilmarth Aldrich (/ˈɑldɹɪt͡ʃ/; November 6, 1841 – April 16, 1915) was a prominent American politician and a leader of the Republican Party in the United States Senate, where he represented Rhode Island from 1881 to 1911.

By the 1890s, he was one of the "Big Four" key Republicans who largely controlled the major decisions of the Senate, along with Orville H. Platt, William B. Allison, and John Coit Spooner.

Born at Burgess Farm in Foster, Rhode Island, Aldrich served in the Union Army during the American Civil War.

After the war, he worked his way up to become a partner in a large wholesale grocery firm and won election to the Rhode Island House of Representatives.

He served briefly in the Union Army during the American Civil War when he enlisted as a private in Company D of the 10th Rhode Island Infantry on May 26, 1862.

[7][failed verification] On October 9, 1866, he married Abigail Pearce Truman "Abby" Chapman, a wealthy woman with impressive ancestry.

His long tenure in the Senate was assisted by Rhode Island's restriction of the office to property owners and native-born citizens willing to pay a poll tax, and later, by a legislature that gerrymandered in favor of small Republican towns.

[8] By the 1890s, he was one of the "Big Four" key Republicans who largely controlled the major decisions of the Senate, along with Orville H. Platt of Connecticut, William B. Allison of Iowa and John Coit Spooner of Wisconsin.

Aldrich's main power base was his chairmanship of the Senate Finance Committee which oversaw bank regulation and monetary policy.

As co-author of the Payne–Aldrich Tariff Act of 1909, Aldrich removed restrictive import duties on fine art, which enabled Americans to bring in very expensive European artworks that became the foundation of many leading museums.

In 1909, Aldrich introduced a constitutional amendment to establish an income tax, although he had declared a similar measure "communistic" a decade earlier.

A proponent of Progressive Era themes of Efficiency and scientific expertise, he led a team of experts to study the European national banks.

[12] He worked with several key bankers and economists, including Paul Warburg, Abram Andrew, Frank A. Vanderlip, and Henry Davison, to design a plan for an American central bank in 1911.

He played a central role in winning two-thirds Senate approval of the Treaty of Paris that ended the war, and included annexation of the Philippines.

[21] The Nelson W. Aldrich House on 110 Benevolent Street in Providence serves as the headquarters for the Rhode Island Historical Society.

Aldrich Hall at Harvard Business School in Boston, MA was made possible through a gift from John D. Rockefeller and is named in honor of his father-in-law, Nelson W.