Who is Mikael Blomkvist from The Girl with the Dragon Tattoo and what is their importance?

Mikael Blomkvist is a 42-year-old crusading journalist and co-founder of Millennium, a Swedish financial magazine. He has recently been convicted of libelling wealthy financier Hans-Erik Wennerstrom in one of his stories, so he takes an unusual job writing a chronicle of the wealthy Vanger family while secretly investigating the murder of Harriet Vanger more than 40 years ago.