Hari Seldon is a fictional character in the Foundation series of novels by Isaac Asimov. In his capacity as mathematics professor at Streeling University on the planet Trantor, Seldon develops psychohistory, an algorithmic science that allows him to predict the future in probabilistic terms. On the basis of his psychohistory he is able to predict the eventual fall of the Galactic Empire and to develop a means to shorten the millennia of chaos to follow.

In the first five books of the Foundation series, Hari Seldon made only one in-the-flesh appearance, in the first part of the first book (Foundation), although he did appear at other times in pre-recorded messages to reveal a "Seldon Crisis". After writing five books in chronological order, Asimov wrote two prequels to expand on the genesis of psychohistory. The two prequels—Prelude to Foundation and Forward the Foundation—describe Seldon's life in considerable detail. He is also the central character of the Second Foundation Trilogy written after Asimov's death (Foundation's Fear by Gregory Benford, Foundation and Chaos by Greg Bear, and Foundation's Triumph by David Brin), which are set after Asimov's two prequels.

Seldon is voiced by William Eedle in several episodes of the 1973 BBC Radio 4 adaptation The Foundation Trilogy, and portrayed by Jared Harris in the 2021 Apple TV+ television series adaptation Foundation.

Hari Seldon is first mentioned in the short story "Foundation", published in Astounding Science Fiction in May 1942, as the creator of psychohistory, and appears as a prerecorded hologram near the end. The story was renamed "The Encyclopedists" and collected with four others as Foundation in 1951. "The Psychohistorians" depicts Seldon put on trial by the Commission of Public Safety for his dire predictions about the eventual fall of the Galactic Empire, after which he is exiled to the distant planet Terminus. Seldon's prerecorded messages continue to appear in Foundation and Empire (1952) and Second Foundation (1953), as well as the later sequels, Foundation's Edge (1982) and Foundation and Earth (1986). He is featured as the main character in Asimov's two prequels, Prelude to Foundation (1988) and Forward the Foundation (1993).

Describing "The Psychohistorians" as "28 pages of nonstop world-building", Josh Wimmer and Alasdair Wilkins of Gizmodo wrote that in the story, "Hari Seldon isn't so much a character as he is the living embodiment of psychohistory, an ethereal presence who's about as relatable as Gandalf. It wouldn't be until Prelude to Foundation ... that Seldon would become an actual character."

Galactic Empire First Minister and psychohistorian Hari Seldon was born in the 10th month of the 11,988th year of the Galactic Era (GE) (−79 Foundation Era (FE)) and died 12,069 GE (1 FE).

He was born on the planet Helicon in the Arcturus sector where his father worked as a tobacco grower in a hydroponics plant. He shows incredible mathematical abilities at a very early age.

HARI SELDON–… born in the 11,988th year of the Galactic Era; died 12,069. The dates are more commonly given in terms of the current Foundational Era as −79 to the year 1 F.E. Born to middle-class parents on Helicon, Arcturus sector (where his father, in a legend of doubtful authenticity, was a tobacco grower in the hydroponic plants of the planet), he showed amazing abilities in mathematics from an early age. Anecdotes concerning his ability are innumerable, and some are contradictory. At the age of two, he is said to have …