Nathaniel Prentice (or Prentiss) Banks (January 30, 1816 – September 1, 1894) was an American politician from Massachusetts and a Union general during the Civil War. A millworker, Banks became prominent in local debating societies and entered politics as a young adult. Initially a member of the Democratic Party, Banks's abolitionist views drew him to the nascent Republican Party, through which he won election to the United States House of Representatives and as Governor of Massachusetts in the 1850s. At the start of the 34th Congress, he was elected Speaker of the House in an election that spanned a record 133 ballots taken over the course of two months.

At the outbreak of the Civil War, Abraham Lincoln appointed Banks as one of the first political major generals, over the heads of West Point regulars, who initially resented him, but came to acknowledge his influence on the administration of the war. After suffering a series of inglorious setbacks in the Shenandoah River Valley at the hands of Stonewall Jackson, Banks replaced Benjamin Butler at New Orleans as commander of the Department of the Gulf, charged with the administration of Louisiana and gaining control of the Mississippi River. He failed to reinforce Grant at Vicksburg, and badly handled the Siege of Port Hudson, taking its surrender only after Vicksburg had fallen. He then launched the Red River Campaign, a failed attempt to occupy northern Louisiana and eastern Texas that prompted his recall. Banks was regularly criticized for the failures of his campaigns, notably in tactically important tasks, including reconnaissance. Banks was also instrumental in early reconstruction efforts in Louisiana, intended by Lincoln as a model for later such activities.

After the war, Banks returned to the Massachusetts political scene, serving in Congress, where he supported Manifest destiny, influenced the Alaska Purchase legislation, and supported women's suffrage. In his later years, he adopted more liberal progressive causes. He served as a United States marshal for Massachusetts before suffering a decline in his mental faculties.

Nathaniel Prentice Banks was born at Waltham, Massachusetts, the first child of Nathaniel P. Banks Sr. and Rebecca Greenwood Banks, on January 30, 1816. His father worked in the textile mill of the Boston Manufacturing Company, eventually becoming a foreman. Banks went to local schools until the age of fourteen, at which point the family's financial demands compelled him to take a mill job. He started as a bobbin boy, responsible for replacing bobbins full of thread with empty ones, working in the mills of Waltham and Lowell. Because of this role he became known as Bobbin Boy Banks, a nickname he carried throughout his life. He was at one time apprenticed as a mechanic alongside Elias Howe, a cousin who later had the first patent for a sewing machine with a lockstitch design.

Recognizing the value of education, Banks continued to read, sometimes walking to Boston on his days off to visit the Atheneum Library. He attended company-sponsored lectures by luminaries of the day, including Daniel Webster and other orators. He formed a debate club with other mill workers to improve their oratorical skills and took up acting. He became involved in the local temperance movement; speaking at its events brought him to the attention of Democratic Party leaders, who asked him to speak at campaign events during the 1840 elections. He honed his oratorical and political skills by emulating Robert Rantoul Jr., a Democratic Congressman who also had humble beginnings. His personal good looks, voice, and flair for presentation were all assets that he used to gain advantage in the political sphere, and he deliberately sought to present himself with a more aristocratic bearing than was suggested by his humble beginnings.

Banks's success as a speaker convinced him to quit the mill. He first worked as an editor for two short-lived political newspapers; after they failed, he ran for a seat in the state legislature in 1844, but lost. He then applied for a job to Rantoul, who had been appointed Collector of the Port of Boston, a patronage position. Banks's job, which he held until political changes forced him out in 1849, gave him sufficient security that he was able to marry Mary Theodosia Palmer, an ex-factory employee he had been courting for some time. Banks again ran for the state legislature in 1847, but was unsuccessful.

In 1848, Banks was victorious in another run for the state legislature, successfully organizing elements in Waltham whose votes were not easily controlled by the Whig-controlled Boston Manufacturing Company. Company leaders could effectively compel their workers to vote for Whig candidates because there was no secret ballot. He was at first moderate in opposition to the expansion of slavery, but recognizing the potency of the burgeoning abolitionist movement, he became more strongly attached to that cause as a vehicle for political advancement. This brought Banks, along with fellow Democrats Rantoul and George S. Boutwell to form a coalition with the Free Soil Party that successfully gained control of the legislature and governor's chair. The deals negotiated after the coalition's win in the 1850 election put Boutwell in the governor's chair and made Banks the Speaker of the Massachusetts House of Representatives. Although Banks did not like the radical Free Soiler Charles Sumner (either personally or for his strongly abolitionist politics), he supported the coalition agreement that resulted in Sumner's election to the United States Senate, despite opposition from conservative Democrats. His role as house speaker and his effectiveness in conducting business raised his status significantly, as did his publicity work for the state Board of Education.

In 1852, Banks sought the Democratic nomination for a seat in the United States Congress. While it was at first granted, his refusal to disavow abolitionist positions meant support was withdrawn by party conservatives. He ended up winning a narrow victory anyway, with Free Soil support. In 1853, he presided over the state Constitutional Convention of 1853. This convention produced a series of proposals for constitutional reform, including a new constitution, all of which were rejected by voters. The failure, which was led by Whigs and conservative anti-abolitionist Democrats, spelled the end of the Democratic-Free Soil coalition.