Iku-Turso is a malevolent sea monster in Finnish mythology.
His appearance remains unclear, but he is described with several epithets: partalainen (the one who lives on the brink, or alternatively, the bearded one), Tuonen härkä (the ox of Tuoni, Death), tuhatpää (thousand-headed), tuhatsarvi (thousand-horned). It was sometimes said that he lived in Pohjola, but that may be because Pohjola was often perceived as the home of all evil.
In some versions of the spell The Birth of Nine Diseases Iku-Turso is mentioned as the father of diseases with Loviatar, the blind daughter of Tuoni, the god of death. The Scandinavian giants had the ability to shoot arrows which caused diseases in people.
This and the fact that þurs resembles Tursas gives credence to the idea that they may be related. Some runes tell that Meritursas partalainen makes pregnant the Ilmatar. She later gave birth to Vainamoinen, which would make him a truly primeval creature. On the other hand, he is also mentioned as the son of Ukko (a name usually assigned to the God of Sky).