OK. Who did Calvin murder? And how did he murder them? Be sure to exclude any person lawfully convicted of a capital crime. Even if you think that the crime should not have been a crime.
And it should be noted that even if he were a "murderous tyrant" that really has no bearing on the veracity or falsehood of his statements. Why don't you deal with what he actually says if you wish to discredit him.
You apparently know little to nothing about John Calvin.
Google "The atrocities of John Calvin" there is enough there to keep you reading for the rest of the day.