Tar-Ardamin (S.A. 2618 - 2899, r. 2825 - 2899), Ar-Abattârik in Adûnaic, is sometimes listed in the list of rulers of Númenor but is sometimes omitted. He was the son of King Tar-Calmacil, and if he is counted as one of the rulers, then he is the 19th in the line of rulers. In Adûnaic his name means "Pillar of the World"; in Quenya, it may mean "First of the World".
Tar-Ardamin is omitted in the list of rulers of Númenor in Appendix A of The Lord of the Rings, but is mentioned briefly in Unfinished Tales. J.R.R. Tolkien's son Christopher Tolkien, who compiled and edited Unfinished Tales, speculates in an endnote to the chapter "The Line of Elros: Kings of Númenor" that Tolkien may have had a reason behind the omission that he never elaborated on.
Tar-Ardamin's son, Ar-Adûnakhôr, is generally counted as the 20th ruler.