Yep, Nico Robin, but everyone calls her "Robin" for short, much like "Monkey D. Luffy" is called "Luffy", "Roronoa Zoro" is called "Zoro", and "Tony Tony Chopper" is called "Chopper". In fact, I don't think we've ever found out Nami, Ussop, Sanji, Franky, and Brook's last/first names (depending on Japanese or Western name ordering).
Nico Robin was also known as "Ms. All Sunday" when she was working for Baroque Works in the Alabasta Arc. 4Kids changed it to just "Ms. Sunday", though, and they also gave her a country accent due to the cowboy-esque hat she wore at the time. But after joing the crew of the Going Merry, she's donned many different outfits, just like Nami. Luckily 4Kids lost the rights and the One Piece dub has been picked up by Funimation, and they're doing a superb job with it, I must say.
F.Y.I., official records state that Robin's bust is bigger than Nami's, at least according to their B-W-H measurements (courtesy of Eiichiro Oda, creator of One Piece). Hang on, let me look 'em up... Robin: B99 W59 H89 (39-23-35") Nami: B95 W55 H85 (37-21-33") Heh... Odd... Robin is bigger in all three measurements by exactly 4 centimeters/2 inches...
Though, interestingly enough, as an arc goes on, Nami's bust slowly gets bigger, then resets at the start of the next arc. It's much more noticeable in the manga. Oda, you pervy bastard...