The thing that's so amazing about this show is that prior, you didn't know 1 actor beside Dinklage. Now you're seeing most of them pop up everywhere. The biggest one I've seen in at least 4-5 shows already is Pedro Pascal, https://www.imdb.com/name/nm0050959/?ref_=tt_cl_t1
He has plenty of credit prior to GoT, but I don't recall ever seeing him before.
The only actors I recognized from the GOT pilot episode were Lena Headey, Sean Bean and Jason Momoa. Everyone else was a total unknown to me.
Later on I found out that Peter Dinklage had done a few things before GOT but I didn't watch any of them.
oh yeah, I forgot all about Sean Bean, he's been in a bunch of TV shows, though they never seem to last more than one season