'Game Of Thrones': Don't Call A Tow Truck ... Call 'The Mountain'

Here's Hafpor Julius Bjornsson -- better known as "The Mountain" from "Game of Thrones" -- pulling a 17-TON BIG RIG in Iceland like it was a Tonka Truck.

Yeah, High Sparrow's in trouble ...

Hafpor was training in Iceland for the upcoming Arnold Strongman Classic when he decided weights weren't good enough ... he wanted something much MUCH heavier.

He chose the truck ... and we're told the 6'9", 400 lb monster didn't just pull it once ... we're talkin' multiple laps!

Sources close to Hafpor also tell us everyone at TMZ Sports is frightened of him (they didn't but it's true).

Watch the video and you will be too.