Robert Traill Spence Lowell IV (/ˈloʊəl/; March 1, 1917 – September 12, 1977) was an American poet. He was born into a Boston Brahmin family that could trace its origins back to the Mayflower. His ancestors and contemporary family were important subjects in his poetry. Growing up in Boston also informed his poems, which were frequently set in Boston and the New England region. Literary scholar Paula Hayes argues that, particularly in his early work, Lowell mythologized New England.

Lowell stated, "The poets who most directly influenced me ... were Allen Tate, Elizabeth Bishop, and William Carlos Williams. An unlikely combination! ... but you can see that Bishop is a sort of bridge between Tate's formalism and Williams's informal art." Lowell wrote in both formal, metered verse as well as free verse; his verse in some poems from Life Studies and Notebook fell somewhere in between metered and free verse.

After Life Studies (1959) was published, winning the 1960 National Book Award and featuring "a new emphasis on intense, uninhibited discussion of personal, family, and psychological struggles", he started to be considered an important part of the confessional poetry movement. However, much of Lowell's work, which often combined the public with the personal, did not conform to a typical "confessional poetry" model. Instead, Lowell worked in a number of distinctive stylistic modes and forms over the course of his career.

He was appointed the sixth Consultant in Poetry to the Library of Congress, where he served from 1947 until 1948. In addition to the National Book Award, he won the Pulitzer Prize for Poetry in 1947 and 1974, the National Book Critics Circle Award in 1977, and a National Institute of Arts and Letters Award in 1947. He is "widely considered one of the most important American poets of the postwar era." His biographer Paul Mariani called him "the poet-historian of our time" and "the last of [America's] influential public poets."

Lowell was born to United States Navy Cmdr. Robert Traill Spence Lowell III and Charlotte Winslow in Boston, Massachusetts. The Lowells were a Boston Brahmin family that included poets Amy Lowell and James Russell Lowell; clergymen Charles Russell Lowell Sr. and Robert Traill Spence Lowell; Civil War general and war hero Charles Russell Lowell III (about whom Lowell wrote his poem "Charles Russell Lowell: 1835-1864"); and the Federal Judge John Lowell.

His mother was a descendant of William Samuel Johnson, a signer of the United States Constitution; Jonathan Edwards, the Calvinist theologian (about whom Lowell wrote the poems "Mr. Edwards and the Spider", "Jonathan Edwards in Western Massachusetts", "After the Surprising Conversions", and "The Worst Sinner"); Anne Hutchinson, the Puritan preacher and healer; Robert Livingston (who was also an ancestor on Lowell's paternal side); Thomas Dudley, the second governor of Massachusetts; and Mayflower passengers James Chilton and his daughter Mary Chilton. Lowell's parents share a common descent from Philip Livingston, the son of Robert Livingston, and were sixth cousins.^{[citation needed]}

As well as a family history steeped in Protestantism, Lowell had notable Jewish ancestors on both sides of his family, which he discusses in Part II ("91 Revere Street") of Life Studies. On his father's side, Lowell was the great-great-grandson of Maj. Mordecai Myers (father of Theodorus Bailey Myers, Lowell's great-granduncle), a soldier in the War of 1812 and later mayor of Kinderhook and Schenectady; and on his mother's side, he was descended from the German-Jewish Mordecai family of Raleigh, North Carolina, who were prominent in state affairs.

As a youth, Lowell had a penchant for violence and bullying other children.