The article deals with the history of appearance and transformation of folklore characters of Icelandic Yul lads, who bring gifts to children on Christmas Eve. The thirteen Yul lads appear every night beginning from December the 12th in strict order. After presenting gifts to children they wander around the house for two weeks and steal food or lick plates and pots in secret. Each of them has got its name, character and preferences. Transformation of these creatures was happening gradually in Icelandic literature. It would be natural to suppose that these characters have been existing since Iceland settlement, but ancient Nordic Mythology has not got them at all. Yul lads were first mentioned in the poem by Stefán Ólafsson in the 17th century. Their appearance differs from the present one and resembles those trolls living in mountains who are huge and scary. New details in their appearance were born in the poems in the 18th century. They are becoming less frightening. Their number is unstable and is changing in the course of time. The next changing happened in the 19th century. The fairy tales collector Jón Árnason published a fairy tale in his collection where 13 Yul lads were described. This number has become officially recognised. These characters were canonized only in the 20th century. The Icelandic poet, writer and musician Jóhannes Bjarni Jónasson writing poems under the name of Jóhannes úr Kötlum (Jóhannes from Kötlum) in 1932 collected all the versions of fairy tales with Yul lads and created his own image of them which is considered to be canonized in present Iceland.