Malbeth was a Dúnadan of Arthedain, seer and royal counsellor to the king during the reigns of Araphant and Arvedui. Generally called Malbeth the Seer as a result of the extreme amount of foresight he possessed, his foretellings were recorded in the annals of the North-kingdom, two of which (concerning the destiny of the Dúnedain) were recounted in the Red Book.
The first prophesy dealt with the fate of King Arvedui: Malbeth foresaw that Arvedui would either be the last king of Arthedain and the first king of the Reunited Kingdom of Gondor and Arnor; or he would perish, taking the Kingship in the North with him. In the end, the latter vision was true; Arvedui claimed the vacant Throne of Gondor after the death of King Ondoher (TA 1944), but these claims were refused and the throne instead given to the victorious general Eärnil. The Kingdom in the North failed, as Malbeth had foreseen.
The second prophesy remained somewhat mysterious for a thousand years after Malbeth’s death. It mentioned the awakening of dead Oathbreakers, a horn ringing in the haunted hills, and an appointed hour at the Stone of Erech. In TA 3019, after receiving word from Elrond in Rivendell to remember the words of the visionary, Aragorn discovered that the only way to reach Minas Tirith in time to lend aid was to take the Paths of the Dead. With the Grey Company, he passed through the Stone of Erech, summoned the Dead Men of Dunharrow, and defeated the Corsairs threatening Gondor, thus fulfilling the prophesy.