The Faithful was a name given to those of the Dúnedain in Númenor who remained faithful to the Eldar and the Valar against the wishes and urgings of the later Kings of Númenor.

The lords of the Faithful were of the Line of Elros, descended through Tar-Elendil's daughter, Silmarien. They were the Lords of Andúnië and were in close counsel with the king, until later years, though their hearts remained with the Eldar and the Valar.

The Faithful removed themselves to the western most parts of the land of Númenor during the reign of Tar-Atanamir, where few of the King's Men would come. There in Andúnië they still welcomed the Elves at times.

In the days of Ar-Gimilzôr, the Faithful found themselves being persecuted more and more. The Elves came little to Númenor after these years.

In the days of Ar-Pharazôn, the last king, the Faithful had removed to the East of Númenor and settled around the Bay of Rómenna.

The lord of the Faithful, Amandil, foresaw that the king and his men would storm Aman, so he sought out the Undying Lands himself to beg for help from the Valar. He bid his son Elendil and his children Isildur and Anárion to ready their ships to flee Númenor if need be.

Elendil did as his father asked and when the great wave took their lands under the sea, the ships of the Faithful were spared the destruction and were able to settle the realms of the Exiles of Númenor in Middle-earth.
Encyclopedia entry originally written by Nienna-of-the-Valar