Ida Alexa Ross Wylie, known by her pen name I.A.R. Wylie, was an Australian-British-American novelist, screenwriter, short story writer, poet, and suffragette sympathiser who was honored by the journalistic and literary establishments of her time, and received international recognition for her works. Between 1915 and 1953, more than thirty of her novels and stories were adapted into films, including Keeper of the Flame (1942), which was directed by George Cukor and starred Spencer Tracy and Katharine Hepburn.

Iamblichus was a Syrian neoplatonic philosopher of Arabic origin. He determined a direction later taken by neoplatonism. Iamblichus was also the biographer of the Greek mystic, philosopher, and mathematician Pythagoras. In addition to his philosophical contributions, his Protrepticus is important for the study of the sophists because it preserved about ten pages of an otherwise-unknown sophist known as the Anonymus Iamblichi.

John Watson, was a minister of the Free Church of Scotland. He is remembered as an author of fiction, known by his pen name Ian Maclaren.

Ida Husted Harper was an American author, journalist, columnist, and suffragist, as well as the author of a three-volume biography of suffrage leader Susan B. Anthony at Anthony's request. Harper also co-edited and collaborated with Anthony on volume four (1902) of the six-volume History of Woman Suffrage and completed the project by solo writing volumes five and six (1922) after Anthony's death. In addition, Harper served as secretary of the Indiana chapter of the National Woman Suffrage Association, became a prominent figure in the women's suffrage movement in the U.S., and wrote columns on women's issues for numerous newspapers across the United States. Harper traveled extensively, delivered lectures in support of women's rights, handled press relations for a women's suffrage amendment in California, headed the National American Woman Suffrage Association's national press bureau in New York City and the editorial correspondence department of the Leslie Bureau of Suffrage Education in Washington, D.C., and chaired the press committee of the International Council of Women.

Idah Meacham Strobridge was an American writer and bookbinder. Known primarily for a trio of works about the Great Basin which mix folktales, fiction, sketches, and nature writing: In Miners' Mirage-Land (1904), The Loom of the Desert (1907) and The Land of Purple Shadows (1909).

Charles Ignatius Sancho was a British abolitionist, writer and composer. Born on a slave ship in the Atlantic, Sancho was sold into slavery in the Spanish colony of New Granada. After his parents died, Sancho's owner took the two-year-old orphan to Britain and gifted him to three Greenwich sisters, where he remained for eighteen years. Unable to bear being a servant to them, Sancho ran away to the Montagu House in Blackheath where John Montagu, 2nd Duke of Montagu taught him how to read and encouraged Sancho's budding interest in literature. After spending some time as a butler in the household, Sancho left and started his own business as a shopkeeper, while also starting to write and publish various essays, plays and books.

Immanuel Kant was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and aesthetics have made him one of the most influential figures in modern Western philosophy.

Irvin Shrewsbury Cobb was an American author, humorist, editor and columnist from Paducah, Kentucky, who relocated to New York in 1904, living there for the remainder of his life. He wrote for the New York World, Joseph Pulitzer's newspaper, as the highest paid staff reporter in the United States.

Irving Babbitt was an American academic and literary critic, noted for his founding role in a movement that became known as the New Humanism, a significant influence on literary discussion and conservative thought in the period between 1910 and 1930. He was a cultural critic in the tradition of Matthew Arnold and a consistent opponent of romanticism, as represented by the writings of Jean-Jacques Rousseau. Politically he can, without serious distortion, be called a follower of Aristotle and Edmund Burke. He was an advocate of classical humanism but also offered an ecumenical defense of religion. His humanism implied a broad knowledge of various moral and religious traditions. His book Democracy and Leadership (1924) is regarded as a classic text of political conservatism. Babbitt is regarded as a major influence over American cultural and political conservatism.

Addison Irving Bacheller was an American journalist and writer. He founded the first modern newspaper syndicate in the United States.