The Harbingers of Fate (often referred to as just the Harbingers) is the name of the secret society centered in Absalom dedicated to bringing about the promised Age of Glory by making the prophecies from the ancient Book of 1,000 Whispers come true.1
The Harbingers were founded in 4648 AR by Lord Garron, an exiled Chelish noble living in Absalom who believed that the disappearance of Aroden and the Age of Lost Omens were a mistake on a cosmic level. He believed that bringing about the prophecies foretold in writings called the Book of 1,000 Whispers would somehow re-trigger the promised Age of Glory and perhaps even bring about the return of Aroden himself. The book's predictions were accurate up to the beginning of the Age of Lost Omens, when like all other soothsaying, they no longer came true. Garron believed that the prophecies told the true history of Golarion as it should have happened. Until his death, Lord Garron actively tried to bring about these prophecies in an effort to jump start the promised Age of Glory, but never achieved any positive results.21
His work was continued by his daughter, Lady Arodeth, who has used her fortune to hire agents who scour Avistan and Garund for any clues that might refer to one of the predictions. Their methods grew more and more desperate, as the book's final pronouncements were supposed to occur in 4714 AR. With each passing year and each passing failure, the group strayed further from the teachings of Aroden and deeper into desperation and madness.1 Their goals are not known to the general public, who believe Lady Arodeth to simply be the uninspired inheritor of a mercenary company known as the Band of Blades.3
Now that the year of the final prophecy in the Book of 1,000 Whispers has passed and the Age of Glory has not begun, it is unknown whether the Harbingers are still active.
Paizo published an article about the Harbingers of Fate in Disciple's Doctrine 10f.
For additional as-yet unincorporated sources about this subject, see the Meta page.