from The Pre- and Proto-historic Finns Both Eastern and Western with the Magic Songs of the West Finns by John Abercromby
As the name implies, Ilmarinen, the diminutive of Ilmari, was connected with the air and weather (Ilma). And there is reason, I think, to believe that he was the old air and sky god of the Finns before they ever came in contact with Europeans. Ilmari corresponds formally with the Votiak Inmar, whose name is now used to denote the monotheistic god of the Russians and of the Tatars, but in one district the word has its older meaning of the ‘sky or heaven’ as well, just as tängri signifies ‘god and sky’ among the Turkish tribes of the Altai. In other places in(m) is employed without the suffix –ar for ‘God’ and ‘sky.' Inm is therefore the equivalent of ilma, which, before the Lithuanian term taivas‘sky’ was borrowed, included this meaning as well as ‘air’ and ‘weather.’ Then the Lapps at a comparatively recent period borrowed the name of Ilmarinen under the form of Ilmaris, and sometimes drew his portrait on their magic drums. But it is to be observed that they did not regard him as a smith, but as a god that could produce storms and bad weather. On a magic drum he takes the place usually occupied by the native wind god. This conception of him agrees on the whole with Bishop Agricola’s description in the middle of the sixteenth century. He terms him a god of the Tavastlanders who made calm and weather (ilma) and led travelers forward.
It would seem that though Ilmarinen was best known as the wonderful smith, he was still regarded as an air and storm god as late as the middle of the sixteenth century. The transference from one character to another is not difficult to imagine. We may suppose that at some time not earlier than the fourth or fifth century, when the Finns had become familiar with the smith’s craft, the clang of the hammer on the anvil and the sparks flying from the hot iron struck someone as flashing of lightning. So the air god, when thundering in the clouds and launching forth his fire, became gradually assimilated with a human smith working in his forge. In this way he acquired a new anthropomorphic character and eventually became more and more separated from his aspect of the thunder and storm spirit, which was continued under the newer appellation of Ukko the ‘old man.’
The original character of Ilmarinen comes out when he, together with Väinämönen and the aerial god, is invoked by an exorcist to come to crush a malady, personified as the evil spirit, Hiisi. Again, fire is said to have originated from a spark struck in the sky by Ilmarinen and Väinämönen, which afterwards fell to earth. And a riddle runs thus: ‘Ilmarinen struck fire, Väinämönen caused a flash? Answer. A flash of lightning.’ These two companions together with Lemminkäinen are mentioned as rowing in a red boat towards the north, Ilmarinen taking the bow oar and Väinämönen steering. The story is recited as a charm by persons travelling by water and so has a certain mythological character, but otherwise it has only a slight bearing upon Ilmarinen as an air god.