Ibun and his brother Khîm were the sons of Mîm, the petty-dwarf that led Túrin and the outlaws to Amon Rûdh. Khîm was slain by Túrin's folk, but Ibun survived and stayed with his father and the outlaws in the House of Ransom.

Ibun was taken captive by Orcs when gathering roots with his father. Mîm then decided to lead the Orcs to Amon Rûdh for a sort of ransom so that he could be let free, so betraying Túrin. It is likely that Ibun did not survive their capture because later, when Mîm met Húrin, Mîm said that he was the last of his folk.