The thirteenth Chieftain of the Dúnedain, who inherited the title on the death his father Arathorn I. Little of consequence is recorded as occurring in the northern lands during the time of his rule (except perhaps the birth of Bilbo Baggins in the Shire). The most significant event of Argonui's time as Chieftain came at the end of his rule, when the Fell Winter descended on Middle-earth. Argonui died the year after this time of hardship, though whether his death was directly due to the terrible winter, or the floods that followed it in spring, is not known.
The date of Argonui's birth appears only in The History of Middle-earth volume XII, The Peoples of Middle-earth. It cannot therefore be considered completely reliable.
Argonui's name may contain a derivation from gond 'stone', and may also incorporate nui 'beneath'. Thus his name might conceivably be interpreted as 'king beneath stone'. Lacking biographical details for this Chieftain, it's impossible to be sure whether this interpretation would be meaningful, and Argonui's name ultimately remains obscure.