Finnic religion before Christianity was not built around a court of moralizing gods so much as around the idea that every domain a person depended on had an owner whose permission mattered. The forest belonged to Tapio, grey bearded and mossclad, and to his wife Mielikki, who was the one hunters more often actually addressed; a hunter who wanted game prayed to them before setting out and thanked them afterward, and the forest itself was called Tapiola, Tapio's own estate.
The waters belonged to Ahti, also called Ahto, and his wife Vellamo, who governed the fish and could raise or calm the waves, so that a fisherman's catch was as much a grant as a haul. Death had its own household too: Tuoni and Tuonetar presided over Tuonela, the river-bound land of the dead that Vainamoinen crosses and barely recrosses in the Kalevala, and Kalma, whose name is the ordinary Finnish word for both a grave and the smell of death, was addressed directly in healing charms rather than met in narrative.
Standing over all of them was Ukko, the old man of the sky, thunder and rain, on whom the harvest depended and to whom the spring festival Ukon vakat was kept with ale drunk for good weather; Christian mission absorbed his name into the word for the Devil while the ordinary Finnish word for thunder, ukkonen, still carries him in it. What survived Christianization was not a coherent theology so much as this pattern of addressed, propitiated owners, which is why folk charm and folk custom kept traces of the old gods for centuries after formal worship had ended.