Viggo was just Like That™ for the whole trilogy, taking method acting to extreme levels:
he would spend multiple days walking overland to locations in full pack, sword, & armour when everyone else was travelling in trucks
refused to use any prop swords that weren’t actual steel
basically lived in the forest in-costume, sleeping rough under the sky, even fishing & foraging for his food when possible
often spent hours in the barn just bonding with the horses. He adopted the horse he rode, Uranus, after filming ended
repaired all his own gear by hand, which was often since he never took it off
had a tooth knocked out during filming but had the crew simply glue it back in place so they could keep filming
the instructor who taught everyone swordplay said Viggo was the best swordsman he had ever trained
carried his sword literally everywhere & practiced non-stop, resulting in the cops being called when locals reported “a wild man swinging a sword around his head" outside a gym in Wellington
an orc actor fucked up & accidentally threw a dagger directly into Viggo’s face, but Viggo just deflected it with his sword. They kept that shot
infamously broke 3 toes kicking that helmet but stayed in-character & sold his very real scream as part of the scene. They also kept that shot
Viggo insists on doing his own stunts; in The Two Towers where Aragorn is unconscious & floating down the river, the strong current pulled him underwater for so long that a rescue team had to go in to save him. Viggo survived by grabbing a boulder on the riverbed and pulling himself to the surface
It’s probably more accurate to say that Aragorn played Viggo Mortensen in the off season, so I’m 100% unsurprised to hear he put a whole crowd of fellow actors in genuine mortal peril for a 12% increase in authenticity