"It" from Abruptum was a mystery of the black metal scene. Some creature without the name, non-human, something that you can't describe. There are many legends about this interesting character from the underground music.
Swedish band Abruptum is one of the most atmospheric and non-commercial projects in the black metal scene of 90th. Their sound even not a clear black metal it's could be described as the black metal/ambient/noise. And when you listen to some of their albums, you could feel the horror atmosphere. As I heard about them, "It" was the part of Abruptum, who brought black metal sound to Abruptum ("Evil" always sought to experimental industrial sound).
The legendary of Abruptum began because these guys tried to create most satanic, most horrific black metal band in the world. Each album was like an antichristian kick. So, weird and scary members of the band were part of the full picture that called Abruptum.
"It" was a founder of Swedish satanic organization, called "The True Satanist Horde". Some of his fans thought that he was a great philosopher, but I do not agree with this opinion.
Also, "It" (Tony Särkkä) had a problem with another satanist organization and members of this organization threated that they will kill him. And seems like he was not so fearless guy, and he left the band and the country.
Then he played in other black metal and non-black metal bands, the most famous is Ophthalamia.
The reason for his death was not official apprised, but it looks like his death was non-violent.
Also, Abruptum made excellent track for the tribute to Euronymous "De Profundis Mors Vas Counsumet"
P.S.: if you don't know Abruptum music, I advise you start listening from "Evil Genius" album.