Sean A.P. Ryan: mercenary,self-described cleanser of the gene pool, and he lists his resume in terms of property damage and body counts.
While blunt, Ryan doesn't necessarily have to be evil. After all, you have comic book characters like Wolverine who slash hordes to pieces all the time, and his kill count is probably somewhere in the thousands by now ... assuming he doesn't get rebooted into being a hippy....
But I digress.
However, in the case of Sean Ryan, he's working for the Vatican ... he's supposed to be training priests and nuns in nonlethal combat. His third scene in the novel has Sean crippling an opponent -- not many people recover well from a shattered kneecap.
And people wonder why I make the Pope a suspect in A Pius Man ... if he's hired this lunatic, almost nothing could be put past him.
But, do you necessarily need violence for a good, intimidating character? Heck no. All you need is the implication that there will be very, very, very bad things that happen if someone crosses him/her.
Frankly, all you need is a reputation.
For example, take a clip from the tv show Doctor Who -- a series about a time traveling alien (there's a reason why there are Romans and spaceships in the same scene) ....
This is someone who has a reputation and is not afraid to use it.