The son of ChieftainArador of the Dúnedain, and a descendant through many generations of Isildur himself. Of Arathorn's early life, little is known. He first appears in annals at the age of fifty-six, seeking the hand of Gilraen as his wife. Gilraen at that time was just twenty-two years old, and though the wedding was at first opposed by her father Dírhael, she became Arathorn's wife.
Tolkien reveals something of the etymology of Arathorn's name in a late letter: 'The name contains an abbreviated form of þorono (thorono) 'eagle', seen in Thoron- dor, Thorongil...' (The Letters of J.R.R. Tolkien, No 347, dated 1972).