What was so terrible about Ivan the Terrible?

Answer 1

extract from link below.

The Russian word grozny (as in "Ivan Grozny") means "terrible" in our modern American sense of "extremely not nice," and that certainly applies to Ivan IV (1530-1584), the bloodiest ruler in Russian history before Joseph Stalin, a man who killed his son in a fit of anger and who went through more wives than his approximate contemporary Henry VIII of England. But grozny also means "awe-inspiring" -- that which provokes reverence or terror. This meaning of the word also applies to Ivan, the first man who brought the vast Russian territory under a single, strong rule and the first who publicly claimed or deserved the title "Czar of Russia."

https://www.washingtonpost.com/wp-srv/style/longte...

Answer 2

He had a really mean stare