Hari Seldon

On Trantor, Hari announces that the Empire will fall. He doesn't promise to save anything: the collapse is certain, and the only thing left to change is how long the chaos lasts afterward. Tried for treason, he offers a way out: take his followers to Terminus, at the edge of the Galaxy, to preserve human knowledge and shorten the dark age from 30,000 years to one thousand. After the attack on the Star Bridge, Brother Day agrees to the exile. To Hari, Gaal matters: he brought her from Synnax because she can check math no one else understands.

On the voyage, Raych, Hari's adopted son, kills him. It was part of the plan: Hari had stored his mind in the Prime Radiant. One copy of him finds Gaal and tells her what he planned.

Hari planned even his own burial: his casket, launched into space, became the Vault of Terminus. For decades, an invisible field around the Vault keeps everyone away except Salvor Hardin. When she solves the first crisis, another copy of Hari appears inside. He talks Anacreon and Thespis into faking their own destruction to fool the Empire, and reveals the Foundation's true purpose.

Trapped inside the Prime Radiant, Hari tries to break out. He gets an organic body and leads Gaal and Salvor to Ignis, home of the Mentalics. Before that, he sends secret instructions to Hober Mallow, the trader who will tip the scales against the Empire. On Ignis, Tellem Bond leaves him to drown in a tidal pool, but he survives. Meanwhile on Terminus, the Vault's Hari faces Brother Day, who has come in person. In the end, after Salvor's death, Hari and Gaal go into cryosleep to wait for the Mule.

Hari and Gaal wake on Ignis 152 years later. The Mentalics have spent that time studying psychohistory and training their powers, and the two get them ready to face the Mule, the deviation the plan never foresaw. On New Terminus, the version of Hari stored in the Vault steps back in when the Mule attacks and drives him off. In the end, that copy asks to go with Gaal, and she says no.

In Isaac Asimov's books, Hari Seldon is the lead of Prelude to Foundation and Forward the Foundation. In the original trilogy, he appears in recordings in the Time Vault at each of the Foundation's crises.