The doll of iban is an item used in the later stages of the Underground Pass quest. It is obtained by searching a chest in Kardia the witch's house deep in the dungeon west of West Ardougne.
The doll is turned into an effigy of Iban by using Iban's shadow, Iban's ashes, Iban's blood and Iban's dove, all of which have to be obtained by completing various tasks in the dungeon, on it. The doll is then thrown down the Well of Voyage at the end of the quest to banish Iban from Gielinor.
If it is lost, speak to the dwarf Niloof to obtain it again. He will also give back the History of Iban.