One definition of tyrant is ‘self made ruler’. The Tsar didn’t make himself, nor did he take power that was not his by tradition.
By contrast, Obama seems to be doing executive orders to add more power to himself.
The Tsar was also head of state of Finland, but that state was not ruled by the Tsar as an autocrat. When the Tsar was murdered, Finland changed their constitution to select a head of state in another way.
Of course, you're gliding over a revolution or two and a civil war that was part of the process.
http://en.wikipedia.org/wiki/Finnish_Civil_War