Adûnakhôr was a Dúnadan, and the twentieth King of Númenor. He became King in 2899.
He was the first King to take his royal name in Adûnaic, the common language of the Dúnedain. It was started by the House of Hador, and thus, strongly influenced by Elvish. It was also called Númenorean. Ar-Adûnakhôr means "Lord of the West", a title that was only given to one of the Valar or to the Elder King himself. The Quenya form of his name was Herunúmen.
He began to persecute the Faithful (the ones in Númenor who still remained faithful to the Valar) and punished those who used the Elvish language openly. From then on the elves did not come to Númenor.