Fornjót was an ancient giant in Norse mythology and a king of Finland. His children are Ægir, the ruler of the sea, Logi the fire giant and Kári the god of wind.

The name has often been interpreted as forn-jótr ancient giant.

Karl Simorck in 1869 identified Formjotr with the primaeval giant Ymir.

But it is also possible, as was suggested by Müller (1818), that it is one of a well-established group of names or titles of gods in -njótr "user, owner, possessor", which would make Fornjótr the "original owner" (primus occupans vel utens) of Norway.