You're probably already frightened of Hafthor Bjornsson if you've watched his role as Gregor Clegane (AKA "The Mountain") in Game Of Thrones. All those muscles aren't just for show, however.
It's pretty simple. If it exists, Hafthor Bjornsson can lift it. Anything that doesn't exist is probably just hiding from him.
No exceptions, as shown here when he competed at -- and spoiler alert, won -- the 2014 European Strongest Man competition. As per his own definition, and I'm certainly not going to argue with him, he is "the future of strength".