Zar Godunov

I recently was looking through my heritage and came across an important man named Boris Godunov, a past Zar (is this correct spelling? or is it Tsar?) of Russia. I was told that he for many years worked with Ivan the Terrible, later was crowned by popular demand on account of Feodor having no children to inherit it. That Boris was later killed by his enemies along side his wife and children in 1605. And that another close relative later traveled to America and changed their name to Godun. And that's how I got my last name. But I believe though that there are many gaps in this time line though and would care for assistance in reconstructing it and possibly reconstructing it.