Question

Which Russian ruler enlarged the Russian empire and the magnificent Catherdal but ruled cruelly

Answer 1

I believe that would be Ivan IV Vasilyevich aka Ivan The Terrible.
Hope it helps!

Answer 2

The name of that Russian ruler is Ivan IV Vasilyevich or Ivan the Terrible. 
The nick name 'terrible' came from his cruel and harsh nature towards all the enemy that he faced.
In the expansion process, he's never had a doubt to killed all the enemies that stand in his way and often use the way of terror to make other kingdom submit.