Short answers, pulled from the story.
The Kalevala is a 19th-century compilation of Finnish, Karelian, and Ingrian epic poetry assembled by Elias Lönnrot. The first version, known as the Old Kalevala, was published in 1835 and contained 12,078 verses. The standard version, published in 1849, expanded to 22,795 verses across fifty poems.
Elias Lönnrot, a physician and linguist born on the 9th of April 1802, compiled the Kalevala. He made eleven field trips over fifteen years across Finland and Russian Karelia, collecting oral poetry from village singers. His fifth trip alone yielded almost 300 poems totalling just over 13,000 verses, partly thanks to two days of continuous recitation by the singer Arhippa Perttunen.
Tolkien claimed the Kalevala as one of his sources for The Silmarillion. The Kullervo story directly underlies the tale of Túrin Turambar in Narn i Chîn Húrin, including the detail of a sword that speaks before a suicide. The character Ilmarinen influenced Aulë, the Lord of Matter, and echoes of Väinämöinen can be found in Tom Bombadil of The Lord of the Rings.
As of 2010, the Kalevala had been translated into sixty-one languages, making it Finland's most translated work of literature. The Kalevala has also been translated more than 150 times in total across those languages.
Kalevala Day is observed on the 28th of February each year, marking the 1835 publication date of Elias Lönnrot's first version of the Kalevala. It is also officially known as Finnish Culture Day.
Finnish historian Väinö Kaukonen estimated that 33% of the Kalevala consists of original, unedited oral poetry, while 50% are verses kept mostly unchanged with minor alterations. The remaining 17% are either Lönnrot's own compositions or lines he constructed by combining poem variants. Lönnrot also merged characters and invented connecting passages to create a coherent narrative.