Ilmarinen is a Finnish, Estonian & Uralic Myth. He has made appearances in books for years. He became more widely known when the National Epic "Kalevala" was published. He was often thought of as a god. His people were a very Shamanistic and thought of the Bear as a very religious icon.
Sources very some but I have combined them here. Ilmarinen's mother was Lakka. Vainamoinen was often called his brother even though Ilmater was Vainamoinen's mother. His sister was Annikki who is also sister to Lemminkainen. Lemminkainen's father is Lempi so is most likely Ilmarinen's as well. Lakka and Ilmater may be considered the same person as well.
Ilmarinen was lead to the land of Pohjola(Northland or Lapland) by his brother Vainamoinen to see the most beautiful woman he had ever seen. The Old Crone of Louhi had demanded a relic called the Sampo and/or trial be done to take her daughter the child of the Hiisi, and since Vainamoinen couldn't make such a thing he brought his brother, Ilmarinen. After seeing the maiden
He was the most gifted Smith to exist. He had discovered Iron and how to work it. He created the Celestial Dome in the sky.
He either built the Sampo or performed impossible tasks to get his most beautiful bride.
It took him seven days of smithing to create the Sampo. He called up the Four Winds to stoke the fires of his furnace. Over the course of those days he created a Golden Crossbow that loved to kill men, a metal ship with gold ribs and copper oars that couldn't wait to go to war, a metal cow with golden horns and the Sun and Stars on its brow and a golden plow and plowshare with copper beams and silver handles. He continued to through back into the fire what he had made and on the seventh day The Sampo was made, it could produce infinite amounts of gold, salt and flour.
Along with this gift he had to perform Impossible tasks that his brother Lemminkainen had already failed doing and was even slain while doing because he too want the Rainbow Goddess for himself, but that is another story. He 1st plows a field of viper, following he hunts the Bear of Tuonela and the Wolf of Manala. He fishes the Great Pike out of the Tuonela River and Captures the Elk of Hissi, but the Elk is slain.
Most stories say he got the girl one way or another. The brothers often didn't take no for an answer and Louhi was not to be trusted.
Sometime after either living in the land of Pohjola or taking his wife home to live with him he was given or bought a young Kullervo as a slave. Kullervo is thought of as cursed for his bad life and his endless rage. Ilpotar, Ilmarinen's wife made fun of Kullervo and did not like him much or maybe she just wasn't nice. Her mother was Louhi who compares with Baba Yaga in Slavic Myths.
She baked a stone in with his bread and his knife broken when he cut it. His knife was his only heirloom he had left from his family which had all been slain before he was sold into slavery. Kullervo was magically gifted and turn the Cows Ilpotar was milking into Bears who mauled and killed her.
Ilmarinen losing his wife ask Louhi for her youngest daughter's hand and they both refused. He takes her home anyways but she insults him so bad that he uses magic to change her into a seagull and abandons her.
Still grief stricken he decided to make himself a wife. He then forged a Golden Bride, a woman made of gold. He found her to not be suitable so he gave her to Vainamoinen who told he to never trust a woman made of gold and had her melted down and turned into trinkets for his people.
At some point he and his brother Vainamoinen and Lemminkainen all find reasons to go to Pohjola and steal the Sampo. Louhi was not good but sometimes not so bad. During this part of the Epic Vainamoinen creates a harp from a giant Pike they killed along the way. His ability is such that only he could play such an instrument and he uses it to charm all of Pojhola including the Crone Louhi, even the gods come to hear it, after he puts them all to sleep. The steal off with the Sampo while everyone is sleeping.
When Louhi awakens she summons a great fog over the sea so the hero's will not be able to navigate. She summons Iku-Turso(a giant octopus monster) and sends it to kill them. Vainamoinen seizes the monster and actually holds it and interogates it. Louhi summons great winds to cause great ocean waves to stop their progress. Vainamoinen tells the waves to stop and they do.
Louhi gathers her army and and tranforms into a giant bird big and eventually carries what's left of her army.She gives chase, Vainamoinen offers to share the Sampo and Louhi refuses and in the struggles is is lost at sea . She later steals the Sun and Moon and sends nine diseases Ilarinen actually forges a new Sun and Moon. They are not as good as the original so Vainamoinen forces Louhi to return the orignals.
In Comics he has made appearances in Dawn as she went to him to have him forge her personal forge as well as Comic Versions of the Kalevala in different countries.
In Comics he has made appearances in Dawn and in other independent companies.
In Marvel comics he has made appearances with others from his mythology.