This I saw for the first time in 2013, in Northern Italy. It was another one I was really excited about, having eluded me on all previous attempts to find it.
In the event, with no reliable site knowledge, and travelling back towards Bergamo for a flight home, a hunch about a spot at the roadside proved to be spectacularly right.
This was patient and well behaved for a short time, but never allowed a view, let alone a photograph of it's underside.... maybe next time !
Indeed there was a next time - in July 2015 I encountered the species again in Northern Italy, hence a further butterfly photograph or three.
In 2018 I encountered the paler, arctic version of Thor's and took two acceptable photographs.
The two below are the Arctic images...