In so far as we know, the answere is no one. Iceland was uninhabited around the time of the norse settlement, at least in terms of indigenous people. There may or may not have been a small settlement of monks on the island at some point before the Norse settlement but there is no archeoligcal evidence of this that I'm aware of yet, just the mention of it in the Landnámabók from the 13th century.
What animal life was present on the island before human settlement?