Tatiana Maslany
Credit: BBC America, Escapist Magazine
Tatiana Maslany has made a film reel for her whole career out of this one show. The makers of Orphan Black dress her up in different styles and she puts on different accents. Regardless of whether you like this show or not, I'd recommend making it through at least the first half of the season to fully enjoy Maslany's tour de force acting.
The only criticism I have, and one that my UK friends point out, is that one of the English accents she uses sometimes sounds a bit Australian. This is a minor flaw that can be easily written off since the show is set in Canada. It is no stretch to assume the character's native accent has mixed with the tones of her new home. Honestly, the more you find out about the character's past, the more you could argue she should have a Canadian accent.
Hands down Maslany is one of the most impressive actresses of our generation. I hope she ends up with way more awards then the entire cast of The Big Bang Theory. Even though this is something she has repeatedly stated as being a low priority for her.