I think if Matt Damon & Ben Affleck. Since they are both from that area, they really like to play up the Boston accent, too. I think Matt used it in
The Departed.
Hugh Laurie for me. I've probably seen him before
House, M.D. But, I wouldn't have been able to pick him out of a police line up. So, really the first time I saw him was as House.
Also Freddie Highmore. I didn't even know he was a Brit till Vera Farmiga (Norma) said in an interview that Freddie went back to Britain when they weren't filming
Bates Motel, to finish college.
One time I saw a funny outtake, where Freddie couldn't remember his line, and he tried to fill it in and naturally slipped into his own British accent. Vera stared laughing, saying, "Is Norman British now?"